Sift together cocoa and next 3 ingredients in a medium bowl; set aside.
Beat butter and sugar at medium speed with an electric mixer until light and fluffy. Add eggs, 1 at a time, beating until well blended after each addition. Stir in vanilla.
Add cocoa mixture to butter mixture alternately with sour cream, beginning and ending with cocoa mixture. Beat at low speed until blended after each addition. Stir in morsels.
Place 12 paper baking cups in a muffin pan; spoon batter evenly into cups, filling completely full.
Bake at 350° for 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 5 minutes; transfer to a wire rack, and cool 30 minutes or until completely cool. Spread cupcakes evenly with White Frosting.