If you've never had a peanut butter cake — not a chocolate cake with peanut butter frosting, but peanut butter through and through, crumb and frosting — you should fix that. It's the kind of dessert that surprises people. They expect a novelty and they get a real cake: tender, deep, almost custardy in the center, with a frosting so silky it falls off the spoon in slow ribbons.
Engineer-brain note: this recipe is in grams. You can substitute cups (I've included them) but a kitchen scale will give you a noticeably better cake. Baking is chemistry and chemistry doesn't care about your measuring cup tolerance.
Makes one 8-inch layer cake · 12 slices Active time: ~25 minutes · Total: about 1 hour 50 minutes
Ingredients
Cake
- 1⅔ cups (210 g) all-purpose flour
- 3 tbsp (24 g) cornstarch
- ½ tsp baking soda
- 2 tsp baking powder
- ½ tsp salt
- ⅓ cup (80 g) unsalted butter, room temperature
- ⅓ cup (75 g) neutral oil (canola, avocado, or refined coconut)
- ½ cup (100 g) granulated sugar
- ¾ cup (150 g) light brown sugar
- ⅔ cup (150 g) smooth, unsweetened, processed peanut butter
- 3 large eggs, room temperature
- 1½ tsp vanilla extract
- 1 cup (225 g) buttermilk, room temperature
Peanut butter frosting
- 1½ cups (340 g) unsalted butter, room temperature
- 3 cups (375 g) powdered sugar, sifted
- 1 cup (250 g) smooth unsweetened peanut butter
- 2 tsp vanilla extract
- ½ cup (120 g) heavy cream, room temperature
- ½ tsp fine salt
Method
1. Heat the oven to 350°F (160°C / 320°F if convection). Grease and line two 8-inch round pans — bottom-line with parchment circles.
2. Sift the dry. Flour, cornstarch, baking soda, baking powder, salt in a bowl. Whisk to combine. Set aside. The cornstarch is the secret weapon — it tenderizes the crumb by reducing effective gluten formation.
3. Cream the fats and sugars. In a big bowl, combine the butter, oil, both sugars, and the peanut butter. Beat with a stand mixer (paddle attachment) or hand mixer on medium for 3 minutes until light and creamy. You want it pale and fluffy — this is where air gets built in.
4. Eggs, one at a time on low speed, 10 to 15 seconds between each. Don't add them all at once or the emulsion breaks.
5. Vanilla and buttermilk on medium speed until smooth. The batter should look creamy and uniform.
6. Fold in the dry. Switch to a spatula. Gently fold the dry ingredients in until you just can't see streaks of flour. Do not overmix — every extra stroke develops gluten, and that's what makes a tough cake. The shift to hand-folding here is the difference between okay and excellent.
7. Distribute and bake. Divide evenly between pans — a kitchen scale on the pans makes this clinical. Drop each pan lightly on the counter twice to release big air bubbles. Bake 30 to 35 minutes until a toothpick comes out clean or with a few moist crumbs.
8. Cool. 15 to 20 minutes in the pans, then turn out onto a wire rack and cool completely before frosting. Warm cake + frosting = sliding disaster.
Frosting
1. In the bowl of a stand mixer (or large bowl with hand mixer), combine the butter, powdered sugar, peanut butter, vanilla, cream, and salt.
2. Mix on lowest speed for about a minute to incorporate without launching sugar everywhere.
3. Crank to medium-high and beat for a full 10 minutes, scraping down halfway. This is non-negotiable. The long whip is what makes the frosting silky and light rather than dense and greasy. Set a timer and walk away.
4. If the frosting is too firm or has lots of air bubbles: butter or cream was too cold. Microwave 5 seconds at a time, stirring between, until soft enough to mix, then re-whip. If too soft: chill 30 minutes and re-whip.
Assemble
Place one cooled layer on a stand. Top with about a third of the frosting, spread to the edges. Top with the second layer, upside down (gives you a flat top). Crumb coat: thin layer of frosting all over, chill 20 minutes. Then the final coat — generous, swooped, with the back of a spoon for texture or a bench scraper for clean restaurant lines.
Notes from the cook
- Peanut butter matters. Use a processed creamy one — Skippy Natural Creamy or Jif Natural. Stone-ground or oil-separating natural PB has too much oil sitting on top and the cake gets greasy. If all you have is sweetened (regular Skippy/Jif), drop the brown sugar in the cake by 2 tbsp.
- Room temperature everything. Eggs, butter, buttermilk, cream. Cold ingredients break the emulsion. Take everything out an hour before you start.
- Buttermilk substitute if you don't have it: 1 cup whole milk + 1 tbsp white vinegar or lemon juice. Stir, sit 5 to 10 minutes.
- Don't skip the toothpick test. PB cakes look browned on top before the center is done. Trust the toothpick.
Notes to elevate
Push it from a great home bake into something that holds its own next to a pastry case:
- Brown the butter. For the frosting, not the cake. Brown the 1½ cups of butter, cool until just resolidifying, then cream with the other frosting ingredients. Nutty depth that pairs absurdly well with peanut butter.
- Add flaky salt to the frosting. ½ tsp Maldon worked into the final whip. Tiny salt crystals on the tongue against the sweet frosting — restaurant move.
- Soak the layers. Make a quick syrup: ¼ cup water + 2 tbsp sugar + 1 tbsp bourbon, boil, cool. Brush onto cake layers before frosting. Bourbon + peanut butter is a magic combination, and the syrup makes the cake genuinely "melt in your mouth."
- Honey glaze for moister-still version. ¼ cup honey + ¼ cup brown sugar + 2 tbsp butter, boil 30 seconds. Poke holes in cake layers (skewer), drizzle on, let absorb. This is the goopy diner-style version.
- Chocolate ganache drip. 4 oz dark chocolate + 4 oz hot heavy cream, stir until smooth, cool slightly. Pour over the top of the frosted cake and let it slide down the sides. Best photo you'll take all year.
- Toppings that elevate. Chopped roasted peanuts pressed into the lower third of the sides. A single Reese's cup, cut in half, in the center. Or — go classy — gold flakes and a halved fig.
- Plate like a restaurant. Don't slice and serve on a flat plate. Cut a wedge, lay it on its side, smear of ganache on the plate, a few crushed peanuts, one perfect mint leaf or banana chip.
Gluten-free
Swap the flour 1:1 with a quality GF all-purpose blend that contains xanthan gum — King Arthur Measure for Measure or Bob's Red Mill 1-to-1. Don't skip the cornstarch; with GF flour it matters even more.
Differences: the crumb is slightly more delicate and dries out a bit faster — eat within 2 days or store in an airtight container with a slice of bread to keep it moist. The cake might brown a touch more on the surface; if it's browning too fast, tent with foil after 20 minutes.
GF vegan version
This one's a real conversion, but it works beautifully. Peanut butter is already vegan, so the structural challenge is the eggs, butter, buttermilk, and cream. Here's the swap list:
- Butter (in cake) → vegan butter (Miyoko's). Same volume.
- Butter (in frosting) → vegan butter, same volume. Miyoko's is essential here — Earth Balance is too soft and the frosting won't hold its shape.
- Eggs → 3 flax eggs (3 tbsp ground flaxseed + 9 tbsp water, sit 10 minutes until thick and gloopy).
- Buttermilk → 1 cup unsweetened oat milk + 1 tbsp apple cider vinegar, sit 5 minutes.
- Heavy cream → plant-based heavy cream (Country Crock plant cream or Silk Heavy Whipping). Coconut cream works but adds a tropical note.
- Flour → GF 1:1 blend with xanthan gum, same as above.
For the frosting, beat the butter solo for 2 minutes first before adding other ingredients — vegan butter benefits from a head start.
Differences from the original: the cake is slightly denser (flax eggs don't lift as much as real eggs) but still tender thanks to the cornstarch. Vegan butter has less water than dairy butter, so the crumb is a touch drier — the oat milk buttermilk compensates well. The frosting holds together but is less "fluffy"; whip the full 10 minutes anyway. Overall flavor is very close — peanut butter is loud and dominates, so the small textural differences read as "homemade variation" rather than "this is vegan." Honest assessment: 9/10 vs. the original. The only people who'll catch it are pastry chefs.