1. Preheat oven to 350°. Beat butter and cream cheese at medium speed with an electric mixer until creamy. Beat in sugar until light and fluffy. Add eggs, 1 at a time, beating until blended after each addition. Stir in orange zest and juice.
2. Combine flour and next 3 ingredients. Gradually add to butter mixture alternately with sour cream, beating until blended. Spoon batter by rounded tablespoonfuls into lightly greased miniature muffin pans.
3. Bake at 350° for 13 to 15 minutes or until a wooden pick inserted in centers comes out clean. Cool in pans on wire racks 5 minutes. Remove from pans to wire racks, and cool completely (about 30 minutes). Pipe or spread Orange Buttercream onto cupcakes.
Note: To prepare regular-size cupcakes, spoon batter into 2 lightly greased 12-cup muffin pans, filling two-thirds full. Bake at 350º for 22 to 24 minutes or until a wooden pick inserted in centers comes out clean. Cool and decorate as desired. Makes 2 dozen.