PREHEAT oven to 350° F. Paper-line 20 muffin cups.
COMBINE flour, cocoa, baking soda and salt in small bowl. Beat sugar, butter, eggs and vanilla extract in large mixer bowl. Gradually beat in flour mixture alternately with milk. Spoon 1/4 cup batter into each prepared muffin cup.
BAKE for 18 to 20 minutes or until wooden pick inserted in centers comes out clean. Cool in pans for 5 minutes; remove to wire racks to cool completely. Frost with Milk Chocolate Frosting.
FOR MILK CHOCOLATE FROSTING:
MICROWAVE morsels, butter and salt in medium, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until morsels are melted. Transfer to large mixer bowl. Gradually beat in sugar alternately with milk. Stir in vanilla extract.