Keto Rhubarb Cake with Butter Sauce (Easy, Tangy, and Totally Worth It)

If you’ve got rhubarb sitting around and you’re not sure what to do with it, this rhubarb cake with butter sauce is where to start. It’s got that sharp rhubarb flavor, a soft cake texture, and a warm, rich butter sauce that drips through every crumb. And yes, it’s low carb, gluten-free, and good enough to fool people who don’t care about any of that.

This cake is the kind of dessert that reminds you of your grandma’s house, maybe like Oma’s rhubarb cake, but updated to work for your keto goals. It’s not loaded with sugar or flour, but still lands all the right comfort food notes. Add a drizzle of warm rhubarb sauce or even a spoonful of whipped cream, and you’re good to go.

What You’ll Love About This Cake

• It’s simple to make—no fuss, no fancy tools.
• Uses everyday ingredients, nothing weird or hard to find.
• Works as a dessert, snack, or even a breakfast slice.
• It fits low-carb and keto diets without tasting like cardboard.

Ingredients You’ll Need

Let’s break this into two parts: the rhubarb cake and the butter sauce.

For the Keto Rhubarb Cake:

• 2 cups diced fresh rhubarb
• 1 ½ cups almond flour
• ½ cup coconut flour
• 1 cup granulated monk fruit or erythritol
• 4 eggs
• ½ cup sour cream (key for that soft texture!)
• ½ cup melted butter
• 1 tsp vanilla extract
• 1 tsp baking powder
• Pinch of salt

For the Butter Sauce:

• ½ cup heavy cream
• ¼ cup butter
• ¼ cup sweetener (monk fruit or erythritol)
• ½ tsp vanilla

This butter sauce isn’t just an afterthought. It melts over the warm cake and gives it that rich, cozy feeling you want from real rhubarb desserts.

Step-by-Step Instructions For Keto Rhubarb Cake with Butter Sauce

1) Prep Your Rhubarb

Chop the rhubarb into small, even pieces—about ½ inch chunks. If your rhubarb stalks are extra tart or stringy, you can peel the outer layer, but it’s not a must. Toss it with a tablespoon of sweetener and set aside while you get the batter going. This will soften the rhubarb slightly and help cut the sharpness.

2) Make the Batter

In a large bowl, mix the almond flour, coconut flour, baking powder, and salt. In a separate bowl, beat the eggs, sour cream, melted butter, vanilla, and sweetener until smooth.

Combine the wet and dry ingredients and stir just until everything’s mixed. Gently fold in the chopped rhubarb.

It’s not a runny batter—it’ll be thick, like a scoopable dough. That’s normal.

3) Bake It

Pour the batter into a greased 9-inch round or square pan. You could also line the pan with parchment paper to make it easy to lift out. Bake at 350°F (175°C) for 35–40 minutes or until the edges are golden and the center is set. A toothpick should come out clean.

Let it cool slightly in the pan, but it’s best served warm with the butter sauce poured over the top.

Make the Butter Sauce

While the cake is baking, toss the butter, cream, sweetener, and vanilla into a small saucepan. Heat it on medium, stirring often. Let it bubble gently for 3–4 minutes until it thickens slightly. Don’t boil it too hard—you just want it rich and smooth.

Pour the warm butter sauce over slices of the rhubarb cake, or serve it on the side. Either way, it’s what ties the whole thing together.

Why This Cake is good For keto?

So many rhubarb cake recipes rely on sugar to tame the sour kick of rhubarb. This one skips the sugar but still keeps the flavor balanced. The mix of almond and coconut flour gives the cake body without making it dry or gritty. Sour cream keeps it tender (and gives a nod to the classic rhubarb sour cream cake from old cookbooks).

And let’s not skip the butter sauce again—seriously, it’s the part people talk about after the cake’s gone.

If you grew up eating rhubarb cake with cake mix recipe marshmallows (that old-school style where everything was sweet and gooey), this version hits a similar cozy note—without the sugar crash.

More Ways to Enjoy Rhubarb

If this is your first run at low-carb rhubarb desserts, welcome to the club. Rhubarb isn’t just for pie or jam. It’s strong, bold, and plays well with buttery, creamy textures.

Want more ideas? Try these next:

• Make a keto-friendly rhubarb sauce with sweetener and vanilla. Serve it over Greek yogurt or chia pudding.
• Try a rhubarb upside down cake—yes, even that classic Food Network one can be remade low-carb using almond flour and sweetener.
• Slice and freeze fresh rhubarb now, so you’ve got it ready for future rhubarb recipes.

Fruit Plus Rhubarb? Here’s the Trick

Most traditional rhubarb desserts recipes mix rhubarb with other fruit like strawberries or apples. You can do this in keto too—just pick lower-carb fruits like raspberries or a few chopped strawberries. This gives you that nostalgic fruit plus rhubarb combo while staying on track.

Want to keep it pure? Just double the rhubarb and let it do the talking.

Tips for the Best Texture

• Don’t skip the sour cream. It helps with moisture, just like in those old rhubarb sour cream cakes.
• Let the cake rest. Like any almond flour cake, it needs a few minutes to settle before you slice.
• Add chopped nuts. Pecans or walnuts give it a little crunch.
• Cinnamon or nutmeg? A small pinch adds warmth without stealing the show.

Can You Store It?

Yep. The cake keeps in the fridge for up to 4 days. Reheat in the microwave for 10–15 seconds and pour the butter sauce back over the top. Freezing? Go ahead—just wrap tightly and skip the sauce until serving.

Pro tip: Freeze it in individual slices so you don’t have to thaw the whole thing at once.

What Makes This One of the Best Rhubarb Recipes?

It’s not just the taste (though that’s solid). It’s the feeling. A slice of this rhubarb cake butter sauce combo feels homemade, like someone baked it just for you. It’s the keto-friendly version of the best rhubarb recipes your aunt used to bring to church picnics or potlucks.

You don’t need ten ingredients you’ve never heard of. No food processor. No five-step glazes. Just good cake, real butter, and a little bit of love for rhubarb.

Conclusion

If you’ve ever made easy rhubarb recipes and felt like something was missing—this cake fills that gap. It’s easy to mix, quick to bake, and strong enough to hold its own at any family table, keto or not.

Add this to your list of go-to rhubarb desserts recipes. And don’t forget that butter sauce—because once you taste it, you’ll be looking for reasons to pour it on everything.

Now go bake it. You’re gonna want that first warm slice before the rest of the family sniffs it out.

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