Chocolate Chocolate Chip Muffins Gluten free or regular

My daughter is craving those Costco muffins. You know the ones. The ones that are yummy chocolatey on both the outside and inside. I have made them before, just not the gluten-free way. For those of you who are not gluten free, simply use regular all purpose flour and omit the xanthan gum. Otherwise, Follow the recipe. You will be surprised!
Chocolate Chocolate Chip Muffins

1 1/4 cups gluten-free all-purpose flour  (2 parts rice flour, 1 part tapioca flour, 1 part potato starch)
1 tsp xanthan gum
1/2 cup unsweetened cocoa powder
1/2 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon fine salt
2 large eggs
4 tablespoons unsalted butter, melted (room temperature. I made the mistake of having it too hot and ended up with scramble and had to start over. Novice mistake, but I wasn't paying attention.
1/2 cup dark brown sugar
3/4 cup milk
1 tablespoon vegetable oil
2 teaspoons pure vanilla extract
1 cup semisweet chocolate chips

Preheat the oven to 350 degrees F.

Line the muffin tin with paper liners and lightly coat with cooking spray. (if you don't do this the muffins will stick, trust me.)

Whisk the flour, xanthan gum (if gluten free) cocoa, baking powder, baking soda and salt in a medium bowl.

In another medium bowl, lightly whisk the eggs, then whisk in the butter, brown sugar, milk, oil and vanilla.

Quickly fold the wet ingredients into the dry with a rubber spatula. Just before the batter comes together, fold in the chocolate chips—don’t mix the batter too much or the muffins will be tough. Divide the batter among the muffin cups.

Bake until a tester inserted in the center comes out clean, about 25 minutes. Turn the muffins out of the tins, cool on a rack. I store them in the fridge.