Preheat oven to 350°F. Line a 48-cup mini muffin pan or two 24-cup pans with mini cupcake liners.

In a large mixing bowl use a whisk to combine flour, cocoa powder, baking soda, and salt. Add the chocolate chips and stir to coat the chips in flour mixture.

In a separate large mixing bowl use a wire whisk to whisk eggs and sugars until ingredients are combined and sugars are dissolved. Add sour cream, oil, and milk. Whisk again to combine. If using espresso powder, add to vanilla and then add vanilla to wet ingredients. Whisk vanilla espresso mixture into other liquid ingredients.

Pour liquid ingredients on top of dry ingredients. Using a rubber spatula, mix until just combined, being careful to not overmix. Batter should be thick and shiny.

Using a tablespoon or 2 spoons, spoon muffin batter into liners. Batter should be filled almost to top of each liner. If desired, top each muffin with sea salt before baking.

Bake muffins on the center rack 6 minutes. Rotate pan and bake 6 minutes more or until a toothpick inserted in a muffin comes out clean. Place muffin pan on a cooling rack to cool completely. Makes 48 mini muffins. Recipe from Culinary.net.