1Preheat oven to 350 degrees F (175 degrees C). Lightly grease 12 muffin cups.
2In a large bowl, cream together butter and sugar. Beat in eggs one at a time then stir in the milk, yogurt and vanilla. Blend in the flour, then fold in the chocolate chips. Scoop batter into the prepared muffin cups.
3Bake in prepared oven for 15 to 20 minutes. Move to a wire rack to cool.