1-First Step: Preheat your oven to 375°F. Line two baking sheets with parchment paper to prevent sticking and ensure even baking. This setup lets you bake two batches at once for efficiency.

2-Second Step: In a large bowl, whisk together 2 cups flour, ½ cup cocoa powder, and 1 tsp baking soda. Sift if clumpy for smooth batter. This dry mix forms the base of your chocolate cake whoopie pies.

3-Third Step: In another bowl, beat 1 egg with 1 cup sugar until light. Add ½ cup oil, 1 tsp vanilla, and 1 cup buttermilk. Stir until blended. Pour wet into dry, mixing just until combined. Avoid overmixing to keep pies tender.

4-Fourth Step: Chill the batter for 30 minutes in the fridge. This step, a pro tip for even shapes, helps the whoopie pies hold their dome. Scoop 2-tablespoon mounds onto sheets, spacing 2 inches apart. You will get about 24 halves.

5-Fifth Step: Bake for 10-12 minutes until tops spring back when touched. Rotate sheets halfway for uniform browning. Cool on sheets for 5 minutes, then transfer to racks. Full cooling takes 30 minutes before filling.

6-Sixth Step: Beat ½ cup softened butter, 1 cup marshmallow fluff, 1 cup powdered sugar, and 1 tsp vanilla for 3-5 minutes until fluffy. Add 1-2 tbsp milk if too thick. This marshmallow filling is the heart of classic whoopie pies.

7-Final Step: Pair cooled cookies by size. Spread or pipe 2 tbsp filling on flat sides, sandwich gently. Dust with powdered sugar if desired. Store in airtight container. Yields 12 chocolate whoopie pies ready to enjoy.