01 -
Set your oven to 175°C (350°F). Coat two 9-inch round cake pans with butter and a sprinkle of flour.
02 -
Stir together the flour, salt, baking powder, and baking soda in a bowl.
03 -
Use a mixer to beat together the softened butter and peanut butter until it's smooth. Gradually add in the sugar and keep mixing until it looks light and fluffy.
04 -
Crack in the eggs one by one, blending well after each. Pour in the vanilla and mix again.
05 -
Alternate adding the dry mix and buttermilk into the peanut butter mixture. Begin and finish with the dry mix, and stop mixing when everything's just combined.
06 -
Carefully mix in the M&M's using a spatula or spoon.
07 -
Pour the batter into the pans, dividing it evenly. Bake for 25 to 30 minutes, or until a toothpick in the middle of the cakes comes out clean.
08 -
Let the cakes sit in their pans for about 10 minutes, then move them over to a wire rack until fully cooled.
09 -
Beat the peanut butter and butter until they're creamy. Slowly add powdered sugar while mixing. Pour in the cream and vanilla, then continue beating until light and fluffy.
10 -
Spread a layer of frosting over one cake, place the second cake on top, and frost the top and sides evenly.
11 -
Scatter extra M&M's over the top to finish.