In the bowl of a stand mixer fitted with the paddle attachment, cream butter and sugar on medium speed until fluffy. Add egg, egg yolks, and vanilla; mix until well combined. Reduce speed to low; alternate adding flour mixture and milk to mixer, beginning and ending with flour. Fold in chips with a spatula. Divide batter among muffin tins. Bake until light golden and when an inserted wooden toothpick comes out clean, about 30 minutes. Cool in pan 15 minutes.