Preheat the oven to 375 degrees F. Grease a 12-cup standard muffin pan with nonstick spray.
In a medium bowl, stir together the flour, cocoa powder, chocolate chips, baking powder, baking soda, and salt.
Add the yogurt, milk, maple syrup, eggs, butter, and vanilla.
Gently stir or whisk together.
Divide batter among the prepared muffin tin, using a heaping ¼ cup batter in each cup.
Bake for 14-16 minutes, or until the edges are lightly golden brown and a cake tester inserted into the center comes out cleanly.
(To make as mini muffins, use a mini muffin pan, about 1½ tablespoons batter in each muffin cup, and bake for 10-12 minutes.)
Remove from oven, then transfer muffins to a wire rack to cool fully.
