Beat butter at medium speed with an electric mixer until creamy; gradually add sugar, beating well. Add eggs, 1 at a time, beating just until yellow disappears.
Combine flour, baking powder, and soda; add to butter mixture alternately with sour cream, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Stir in vanilla.
Spread half of batter into a greased 9-inch square pan. Sprinkle with chocolate morsels and cinnamon. Spread remaining batter over chocolate layer.
Bake at 350° for 35 minutes or until cake begins to leave sides of pan; cool in pan on a wire rack. Cut into squares.