Cream butter and 4.6 oz. sugar in mixer fitted with paddle attachment until well blended. Add eggs in 2 additions, mixing well after each.
Sift dry ingredients. Combine milk, buttermilk, and vanilla in separate bowl.
Alternate adding shifted dry ingredients and milk mixture, to butter and egg mixture. Mix just to combine after each addition.
Divide batter among lightly greased mini (2-inch) donut pans. Bake in 350°F standard oven 9 to 11 min. or until donuts spring back when lightly touched. Cool in pans on wire rack 3 min. Carefully remove from pans.
While donuts are still warm, dip each into melted butter, then into remaining 2.8 oz. of sugar. Cool completely on wire racks. Plate 2 donuts per serving.