In a large bowl, combine the 1 cup granulated sugar and the butter with an electric mixer until fluffy. Add eggs and beat until combined. Beat in sour cream and vanilla.
Combine the flour, baking powder, baking soda, and salt. Add to the beaten mixture, beating until smooth.
In another mixing bowl, stir together the nuts, semisweet chocolate pieces, the 1/2 cup granulated sugar, the brown sugar, and cinnamon.
Evenly spread half of the batter in a greased 13x9x2-inch baking pan. Sprinkle with half of the chocolate mixture. Top with remaining batter, then the rest of the chocolate mixture.
Bake in a 350 degree F oven for about 40 minutes or until a toothpick inserted in the center comes out clean. Serve warm. Makes 12 to 16 servings.