Oat Orange and Chocolate Chip Muffins

6 tablespoons unsalted butter, room temperature, plus more for tins
2 3/4 cups, plus 2 tablespoons all-purpose flour
1/4 cup oat flour (*See note below on how to make it)
3 teaspoons baking powder
1 teaspoon salt
1 cups white granulated sugar
1/4 cup dark brown sugar 
1 large egg
2 large egg yolks
1 teaspoon pure vanilla extract
1 1/2 tablespoon fresh orange zest
1 cup milk
1/2 cup semi-sweet chocolate chips 
Handful of rolled oats

1. Preheat the oven to 375 degrees. Butter large (3 3/4 inches) or small (2 3/4 inches) muffin tins, and set aside. Or alternatively, line with muffin liners and spray lightly with PAM. 

2. In a large bowl, mix together all-purpose flour, oat flour, baking powder, and salt; set aside.

3. In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar on medium speed until fluffy, about 3 minutes. Add egg, egg yolks, vanilla extract and orange zest; mix until well combined. Reduce speed to low; alternate adding reserved flour mixture and milk to mixer, beginning and ending with flour. Remove bowl from mixer; gently fold in chocolate chips by hand. Divide batter among muffin tins; sprinkle the tops with rolled oats. Bake until light golden, about 45 minutes for large muffins, about 30 minutes for small muffins. Cool in pan 15 minutes. Remove from pan; transfer to wire rack, and let cool completely.

*Note for oat flour: Many grocery stores stock oat flour. To make your own, simply add rolled oats to a food processor and pulse until mixture is finely ground, about 30-40 seconds