10 ounces (1 1/4 cups) plain greek yogurt (I used nonfat)
2 teaspoons vanilla extract
6 ounces bittersweet chocolate, chopped, divided
1 ounce (1/4 cup) cacao nibs
Preheat oven to 375ºF and grease a standard 12-cup muffin tin with nonstick spray.
In a bowl, whisk together the flour, orange zest, baking powder, baking soda, and salt.
In a separate bowl, whisk together the coconut oil and brown sugar until combined. Beat in egg and egg white one at a time, until mixture is smooth. Beat in yogurt and vanilla extract until smoothly combined.
Add the dry ingredients to the wet and fold in just until mostly incorporated. Add 5 ounces of chocolate chunks and cacao nibs and fold in just until all ingredients are evenly combined; the batter will be quite thick.
Divide batter evenly between the prepared muffin cups and sprinkle tops with remaining chocolate chunks. Bake at 375ºF for 18-20 minutes, just until a toothpick inserted into the center of one comes out free of batter.
Cool muffins in pan for 5-10 minutes, and then transfer to a wire rack to cool completely. Store in an airight container at room temperature.