In a small bowl, stir together cocoa, espresso powder, and 2 tablespoons (30 grams) boiling water until dissolved.

In a large bowl, whisk together flour, granulated sugar, brown sugar, baking powder, salt, and baking soda; make a well in center.

In a medium bowl, whisk together banana, oil, sour cream, eggs, and vanilla. Add banana mixture to flour mixture, stirring just until moistened. Stir 1 cup (270 grams) batter into cocoa mixture until combined. Cover and refrigerate batters for at least 1 hour or up to overnight.

Preheat oven to 400°F (200°C). Line every other cup of 2 (12-cup) muffin pans with tulip-style liners.

Using a 3-tablespoon spring-loaded scoop, scoop banana batter (about 45 grams each) into each prepared muffin cup. Using a 1-tablespoon spring-loaded scoop, scoop chocolate-espresso batter (about 15 grams each) onto banana batter. Using 3-tablespoon scoop, top each with another layer of banana batter. Gently tap pans on a kitchen towel-lined counter to settle batter.

Working with 1 muffin cup at a time, using the back of a spoon, make a shallow trench in center of batter in each muffin cup. Using a 2-teaspoon spring-loaded scoop, scoop chocolate-espresso batter (about 10 grams each) onto banana batter. Using a wooden pick, swirl batters together. Sprinkle turbinado sugar onto batter. Fill empty muffin cups halfway with water.

Bake for 5 minutes. Reduce oven temperature to 375°F (190°C), and bake until a wooden pick inserted incenter comes out clean, 15 to 20 minutes more. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on a wire rack. Store in an airtight container for up to 3 days.