American groundnuts (aka hopniss) are a native, vining legume whose edible tubers taste like a cross between boiled peanuts and potatoes. This American groundnut mash recipe flavored with rosemary brown butter is utterly delicious, and tastes better than any mashed potatoes you’ve ever eaten!
A native food you should grow: American groundnuts (Apios americana)
We’ve been singing the praises of American groundnuts ever since we first grew and tasted them years ago.
They’re a low-maintenance, native plant that produces edible tubers, flowers, and beans. They were a staple crop for innumerable indigenous people/nations both before and after first contact with European settlers. If the Pilgrims hadn’t been introduced to the tubers of this plant, they likely would have died of starvation during their first winter here. (Hello, Thanksgiving side dish!)
In addition to a rich and interesting history, they also have a rich and interesting flavor… The cooked, starchy tubers taste like a cross between boiled peanuts and white potatoes.
However, they have 3x the amount of protein as a potato (16.5% of dry weight) and also boast a range of evidence-based medicinal benefits.
So, why aren’t American groundnuts popular today? They take longer to grow than potatoes, their per acre yields are (possibly) lower, and they require a large trellis for their vines to grow.
For a deeper dive into American groundnuts, read our detailed guide How to grow American groundnuts.
However, since you’re currently reading an American groundnut recipe article, we hope you’ve long been sold on this wonderful plant and are now looking for cooking inspiration. If so, read on!
5 things you should know about cooking with American groundnuts
There’s not much information out there about how to cook with American groundnuts. Since we’ve been experimenting with them for a few years now, here are five things you should know if you’ve never cooked with American groundnuts, all of which also pertain to this recipe:
1. American groundnuts contain a sticky latex in the skin.
When you cut into American groundnut tubers, the skins emit a sticky latex that’s difficult to wash off. The most proximate substance we’ve encountered is while processing jackfruit.
You can use cooking oil on a paper towel or cloth to wipe and remove the latex from the blade of your knife or hands. Or just plan for a good bit of scrubbing with warm soapy water.
After you boil American groundnuts, there will also be a film of latex left on the pan around where the water line was.
2. American groundnut tubers on the same plant vary significantly in size.
We grow ‘Nutty #3’ American groundnuts, an improved strain developed in LSU’s breeding programs in the 1980s and 90s. At harvest, our first year tubers (which grow like beads on a string) generally range between 2-10 ounces each. Some of our older 2+ year old tubers have topped 1 pound.
By comparison, wild-foraged American groundnuts are much smaller, usually topping out at around 6 ounces each.
For cooking purposes, we use tubers that are at least 4+ ounces each (minimum size = golfball) since you get more bang for your buck. We use the smaller tubers (under 4 ounces) as “seed” starts for the next year.
We haven’t noticed a discernible difference in flavor or texture between our smaller and larger American groundnut tubers, but we can’t say for certain whether the same holds true for wild-foraged tubers.
3. American groundnuts require a longer cooking time than potatoes.
Even the largest potato can be boiled within about 30 minutes. However, we recommend boiling American groundnuts (regardless of size) for a minimum of one hour before you use them in a recipe — even if there’s some secondary cooking involved in the recipe!
That’s because American groundnuts are legumes, and their tubers have a high lectin content. Lectin can cause upset stomachs (hey, plants can’t run or fight so they have to defend themselves somehow), but cooking breaks down lectin, rendering it inert.
Also, boil your American groundnuts skin-on for best flavor and nutrition. Then, once they’ve cooled, peel them with a carrot peeler.
4. American groundnuts can absorb a LOT of liquid once cooked.
If you’ve ever made mashed potatoes with standard white potatoes, you know that they can absorb a lot of liquid.
Well, the same is true for American groundnuts – perhaps even more so than for potatoes. This mash recipe calls for a lot of milk and half-and-half, but you can opt for the dairy-free alternative of your choice, if preferred. Another option is to use vegetable stock.
5. American groundnuts can dry out quickly and are best served warm
Not that you’d be tempted to serve a cold mash, but we recommend serving American groundnuts warm for best flavor and consistency. If you’re storing your mash in the fridge, simply re-heat it in the microwave, stir, and you’ll be back in business.
American groundnut mash: step-by-step with photos and tips
Full disclosure: almost all of our recipes originate from actual, functional meals because we don’t have time to cook unless our creations also feed us. In this case, we were having friends over for dinner and things were hectic and rushed.
Nevertheless, the recipe turned out great and was reasonably well documented with pictures (ha). Our dinner guests were blown away by how delicious American groundnut mash is — and a bit perplexed they’d never heard of them before or seen them featured on menus at fancy restaurants.
Hopefully, that will change!
Here’s how to make your own American groundnut mash:
1. Boil for 1 hour with skins on (well in advance of meal).
You’ll start by boiling your tubers (with skins on) for one hour. You should be able to easily stick a fork into them when done.
Next, remove the groundnuts from the water and let them cool to the point that you can easily handle them, at least ~15 minutes.
We do this well ahead of time so we’re not rushed.
2. Make rosemary brown butter.
While your American groundnut tubers are cooling, make your rosemary brown butter.
“Brown butter” is butter that’s cooked on a low temperature just beyond its melting point (stirring almost constantly), but long enough for the milk solids to brown/toast. This creates a wonderfully rich flavor.
You add rosemary right at the end once you see the milk solids browning, then you remove the pan from the heat, and strain out the rosemary. If you add your rosemary at the beginning or too early in the process, all the rosemary flavor will burn out.
Rosemary-infused brown butter adds even more dimension and amazing flavor to this recipe.
3. Peel your tubers, then cut them into 1″ chunks.
Use a carrot peeler to peel the skins off your tubers.
Once skins are removed, cut them into 1″ chunks.
4. Cook all ingredients in a pot for about 10 minutes.
Now put all your ingredients together in a large pot and cook them over medium heat for about 10 minutes, stirring regularly to prevent sticking and scalding. This step helps bring all the flavors together while giving your groundnuts a bit more cook time.
Remove from heat and let cool a bit before…
5. Puree in food processor.
Put all ingredients into a food processor and blend until smooth and pureed. Add more milk or half-and-half as-needed to get them blended into a silky smooth mash.
Serve warm! Unlike mashed potatoes, there’s no need for gravy on your mashed American groundnuts. We think the flavors stand on their own.
Recipe: Hopniss / American groundnut mash with brown butter rosemary
American groundnut mash with brown butter rosemary
Way better than mashed potatoes, this American groundnut mash features the savory boiled-peanut like flavor of American groundnuts (aka hopniss) and rosemary brown butter!
- 2 pounds American groundnuts, weighed whole and uncooked
- 2 cups organic whole grass-fed milk (Alt: dairy-free alternative or veggie stock)
- 3/4 cup organic half-and-half (or add same amount of milk for less fat)
- 5 tbsp organic unsalted butter (for rosemary brown butter)
- 1/2 tsp salt (or to taste)
- 3 tbsp fresh rosemary, diced (or 1 tbsp dried)
Boil American groundnuts in water for 1 hour with skins on. Remove from water and let cool.
While groundnuts are cooling, make rosemary brown butter. In small saucepan over low heat, add butter to pan. Once butter melts, keep a close eye and start stirring. Once butter begins bubbling, it won't be long until the milk solids begin to brown/toast. Once you see this reaction take place (see photo in article), remove from heat and immediately add diced rosemary, continuing to stir. Do NOT add rosemary at beginning or flavor will cook out.
Strain and remove rosemary. Set brown butter aside.
Peel American groundnuts with a carrot peeler, then cut them into ~1" chunks. Add all ingredients to pot and cook over medium heat for about 10 minutes, stirring to prevent sticking and scalding on bottom of pan. Remove from heat and let cool until ingredients are warm, not hot.
Pour into food processor and blend until smooth and creamy mash is made. You may need to add more liquid (milk, half-and-half, or subtitute of your choice).
Serve warm! If storing in fridge for later, reheat in microwave just before serving.
What should you serve your American groundnut mash with? We served ours with maitake mushroom steaks, bone-in pork chops, and cranberry relish, but they’re every bit as versatile as mashed potatoes – even though they taste better.