Start by preheating your oven to 350°F (175°C). Combine the all-purpose flour, unsweetened cocoa powder, baking soda, and salt in a large mixing bowl and whisk together.

Cream together the softened unsalted butter and granulated sugar until smooth and fluffy. Add in the large egg and vanilla extract, mixing until fully incorporated.

Alternately add the dry mixture with the buttermilk and evaporated milk, mixing gently until everything is well incorporated.

Drop rounded tablespoons of batter onto a lined baking sheet, spacing them about 2 inches apart. Bake for 10-12 minutes and let them cool on a wire rack.

Prepare the creamy coconut-pecan filling in a medium saucepan over low heat, whisking together the granulated sugar, egg yolks, and softened butter until thickened. Stir in coconut and pecans, then remove from heat and add in the vanilla extract.

Assemble the whoopie pies by spreading coconut-pecan filling on one cake, then pressing another cake on top.

Enjoy your homemade German Chocolate Whoopie Pies, storing leftovers in an airtight container in the refrigerator.