Chocolate Muffins

Preheat oven to 425°F. Coat a 12-cup muffin tin with cooking spray and line with paper liners. 

Whisk all-purpose flour, whole-wheat flour, sugar, cocoa, espresso powder, baking soda and salt together in a large bowl until combined and free of lumps. 

Whisk eggs, yogurt, oil, buttermilk and vanilla together in a medium bowl until combined. Gently stir the egg mixture into the flour mixture until just combined. Pour the batter evenly into the prepared muffin cups (heaping 1/4 cup each). Sprinkle the tops evenly with chocolate chips.

Bake for 5 minutes. Reduce oven temperature to 350°F (do not remove muffins from oven). Bake until a wooden pick inserted in the center of the muffins comes out clean, 15 to 20 minutes. Let the muffins cool in the pan for 10 minutes. Turn out onto a wire rack and cool for about 15 more minutes. Serve warm or at room temperature.