Banana Coffee Whoopie Pies with Marshmallow Filling
Soft banana cake cookies sandwiched with a coffee-marshmallow buttercream. This recipe uses a boxed cake mix as the base, enriched with mashed brown bananas for flavor and moisture. The filling combines creamed butter, marshmallow fluff, and instant coffee dissolved in vanilla extract, creating a sweet and slightly coffee-forward frosting.
Ingredients
- 1 white cake mixvanilla cake mix1:1similar_function
same texture and crumb
- ⅓ cup water
- 2 large eggs
- 3 tablespoons oil
- 2 brown bananas, mashed
- 1 cup unsalted butter, softened
- 1 7 ounce jar marshmallow fluff
- 1 cup confectioners sugar
- 2 teaspoons vanilla extract
- 2 tablespoons instant coffee
- ½ teaspoon table salt
Instructions
- 1
Preheat oven to 350 degrees.
- 2
Combine water, eggs, oil, and cake mix in a bowl. Beat on low speed for 1 minute, then on medium speed for 1 minute.
- 3
Mash bananas and add to batter. Beat on medium speed for 1 more minute.
- 4
Drop batter by tablespoon onto baking sheet.
- 5
Bake for 8-10 minutes. Cool completely.
- 6
Measure vanilla in a small cup. Add instant coffee and stir until dissolved.
- 7
Pour vanilla-coffee mixture into a mixing bowl and cream with softened butter.
- 8
Add marshmallow fluff and salt. Beat until creamy.
- 9
Gradually add confectioners sugar, incorporating completely.
- 10
Sandwich cooled cookies with filling. Store in sealed container.
Tips
Cool cookies completely before filling to prevent melting the frosting.
Good to Know
Sealed container at room temperature for up to 3 days.
Unbaked batter can be refrigerated up to 24 hours. Baked unfilled cookies freeze for 1 month.
Room temperature. Serve as-is or chilled.
Common Mistakes
Underbaking cookies will result in fragile, difficult-to-handle cakes; check at 8 minutes.
Adding sugar too quickly to the filling will cause lumps; incorporate gradually.
Substitutions
same texture and crumb