On low speed, cream butter and sugar until fluffy. Add eggs, one at a time and mix until blended. Sift dry ingredients and add alternately with milk. Add chocolate chips, vanilla and stir in by hand. Grease muffin tins well with butter and grease top surface of pans as well. Pile mix high in each muffin cup. Sprinkle sugar over tops, bake in 375ºF.  oven for 30 minutes. Cool in pan at least 30 minutes.