Peanut Butter M&M Cake

Dense, fudgy, loaded with colorful M&Ms, and packed with creamy peanut butter flavor, this Peanut Butter M&M Cake is the ultimate dessert for chocolate and peanut butter lovers.

This indulgent cake has a rich, tender crumb with plenty of chocolate candies throughout. A creamy peanut butter frosting takes it over the top, while extra M&Ms add a colorful, crunchy finish. It’s perfect for birthdays, parties, potlucks, holidays, or anytime you want a fun dessert that gets everyone excited.

⏱ Recipe Information

Prep Time: 25 minutes
Bake Time: 30–35 minutes
Cooling Time: 1 hour
Total Time: About 2 hours
Servings: 12–16 slices
Difficulty: Easy
Method: Oven-Baked

Ingredients

Peanut Butter M&M Cake

• 2 cups all-purpose flour
• ½ cup unsweetened cocoa powder
• 1½ teaspoons baking powder
• ½ teaspoon baking soda
• ½ teaspoon salt
• ½ cup unsalted butter, softened
• ½ cup creamy peanut butter
• 1 cup granulated sugar
• ½ cup packed light brown sugar
• 3 large eggs, room temperature
• 2 teaspoons vanilla extract
• 1 cup buttermilk
• 1 cup M&Ms, plus extra for topping

Creamy Peanut Butter Frosting

• ½ cup unsalted butter, softened
• ¾ cup creamy peanut butter
• 2 cups powdered sugar
• 1 teaspoon vanilla extract
• 3–4 tablespoons heavy cream or milk
• Pinch of salt

For Decorating

• ½–1 cup M&Ms
• Mini M&Ms, optional
• Chocolate chips, optional
• Chocolate drizzle, optional

Instructions

1. Prepare the Oven and Pan

Preheat your oven to 350°F (175°C).

Grease a 9×13-inch baking pan and line it with parchment paper, leaving some overhang along the sides for easy removal.

Set aside.

2. Combine the Dry Ingredients

In a medium bowl, whisk together:

• All-purpose flour
• Cocoa powder
• Baking powder
• Baking soda
• Salt

Whisk until the cocoa is evenly distributed and there are no large lumps.

Set aside.

3. Cream the Butter, Peanut Butter, and Sugars

In a large mixing bowl, beat the softened butter and peanut butter together on medium speed until smooth and creamy, about 1–2 minutes.

Add the granulated sugar and brown sugar.

Continue beating for approximately 2–3 minutes, until the mixture becomes lighter and fluffy.

4. Add the Eggs and Vanilla

Add the eggs one at a time, mixing well after each addition.

Add the vanilla extract and beat briefly until incorporated.

Scrape down the sides of the bowl as needed.

5. Add the Dry Ingredients and Buttermilk

Add approximately one-third of the dry ingredients to the peanut butter mixture.

Mix gently.

Add half of the buttermilk and mix again.

Continue alternating the dry ingredients and buttermilk, ending with the dry ingredients.

Mix only until the batter is combined.

Do not overmix.

6. Fold in the M&Ms

Add 1 cup of M&Ms to the batter.

Gently fold them in using a spatula.

Avoid excessive stirring, as the candy shells can begin to break and discolor the batter.

7. Transfer to the Pan

Pour the batter into the prepared baking pan.

Spread it evenly with a spatula.

Sprinkle a small handful of additional M&Ms over the top.

Gently press them into the batter so they remain in place during baking.

8. Bake

Place the cake in the center of the preheated oven.

Bake for approximately 30–35 minutes.

Begin checking around 30 minutes.

The cake is ready when:

• The center looks set.
• The edges are slightly pulled away from the pan.
• A toothpick inserted into the center comes out with a few moist crumbs.

Avoid overbaking—the cake should remain rich and fudgy.

9. Cool Completely

Remove the cake from the oven.

Allow it to cool in the pan for approximately 15–20 minutes.

Lift it out using the parchment paper and transfer it to a wire rack.

Allow the cake to cool completely before frosting.

Make the Peanut Butter Frosting

10. Beat the Butter and Peanut Butter

Place the softened butter and peanut butter in a large mixing bowl.

Beat on medium speed for approximately 2 minutes, until smooth and creamy.

11. Add the Powdered Sugar

Gradually add the powdered sugar while mixing on low speed.

Once incorporated, increase the speed to medium and beat until fluffy.

12. Add Vanilla and Cream

Add the vanilla extract and 3 tablespoons of heavy cream or milk.

Beat for another 2–3 minutes.

If the frosting is too thick, add the remaining tablespoon of cream or milk a little at a time.

If it is too thin, add a little more powdered sugar.

13. Frost the Cake

Once the cake has cooled completely, spread the peanut butter frosting evenly over the top.

Use an offset spatula to create smooth swirls or decorative peaks.

14. Decorate With M&Ms

Generously scatter M&Ms over the frosting.

Gently press them into the frosting so they stay in place.

For an extra indulgent finish, drizzle the cake with melted chocolate.

15. Slice and Serve

Allow the frosting to set for approximately 15–20 minutes before slicing.

Cut into squares and serve at room temperature.

Chef’s Tips

Use Room-Temperature Ingredients

Room-temperature eggs, butter, and buttermilk combine more easily and help produce a smoother batter.

Don’t Overbake

The secret to a dense, fudgy cake is taking it out when a toothpick still has a few moist crumbs attached.

Don’t Overmix

Once the flour is added, mix only until everything is incorporated. Overmixing can make the cake tough.

Keep the M&Ms From Sinking

Toss the M&Ms with 1 teaspoon of flour before folding them into the batter. This can help distribute them more evenly.

Use Creamy Peanut Butter

Regular creamy peanut butter works best for a smooth frosting. Natural peanut butter can sometimes separate and produce a less stable frosting.

Flavor Variations

Chocolate Peanut Butter M&M Cake

Add ½ cup chocolate chips to the batter along with the M&Ms.

Mini M&M Cake

Use mini M&Ms throughout the batter for smaller bursts of chocolate in every bite.

Peanut Butter Cup Cake

Fold chopped peanut butter cups into the batter and sprinkle more over the frosting.

Salted Peanut Butter Cake

Finish the frosted cake with a light sprinkle of flaky sea salt.

Triple Chocolate Version

Add chocolate chips to the batter, use chocolate frosting, and finish with M&Ms.

Serving Suggestions

Serve this cake with:

• Vanilla ice cream
• Chocolate ice cream
• Whipped cream
• Warm chocolate sauce
• Caramel sauce
• Extra peanut butter drizzle
• A cold glass of milk

For a party, cut the cake into small squares and arrange them on a platter with extra M&Ms scattered around the serving dish.

Make-Ahead Instructions

The cake can be baked 1 day ahead.

Allow it to cool completely, cover tightly, and store at room temperature.

The frosting can also be prepared a day ahead and refrigerated.

Allow refrigerated frosting to soften at room temperature for approximately 20–30 minutes, then beat briefly before spreading.

Storage

Store the frosted cake in an airtight container.

Room temperature: Up to 2 days.

Refrigerator: Up to 5 days.

For the best texture, allow refrigerated slices to sit at room temperature for about 15–20 minutes before serving.

Freezing Instructions

Freeze the unfrosted cake for best results.

Wrap it tightly in plastic wrap, followed by aluminum foil.

Freezer: Up to 3 months.

Thaw completely at room temperature before frosting and decorating.

Individual frosted slices can also be frozen in airtight containers.

Recipe Summary

This Peanut Butter M&M Cake is everything a peanut butter and chocolate lover could want: rich, dense, fudgy, creamy, and loaded with colorful M&Ms.

The chocolate-peanut butter cake is topped with silky peanut butter frosting and finished with even more M&Ms for a fun, colorful dessert that’s guaranteed to disappear quickly.

Fudgy chocolate cake + creamy peanut butter frosting + colorful M&Ms = pure dessert happiness.