This recipe claimed to make Costco-esque muffins, but I think they are merely average.... so don't get your hopes up too high!
2 1/4 cups all-purpose flour
1 1/2 teaspoons baking soda
In a small bowl, remove two tablespoons of flour from the 2 1/4 cups (now 2 cups and 2 tablespoons remains) and mix with the chocolate chips. Set aside
In a mixing bowl, combine the remaining flour, sugar, cocoa powder, baking soda, and salt.
In a different bowl, whisk together the eggs, sour cream, milk, oil, and vanilla extract. Stir into dry ingredients just until moistened. Fold in chocolate chips/flour mixture.
Fill lined cupcake pans 2/3 full with batter.Bake at 325 degrees for 18-24 minutes. Muffins are done when a toothpick inserted comes out clean. Cool on wire racks. Dust with powdered sugar if desired.