Combine the first 5 ingredients in a medium bowl; stir well. Cut in shortening with a pastry blender until the mixture resembles coarse meal. Stir in pecans.
Combine the milk and egg; stir with a wire whisk until blended. Add to flour mixture, stirring just until blended. Pour the batter into a greased 9 inch round cakepan.
Bake at 375 degrees for 20 to 25 minutes or until a wooden pick inserted in the center comes out clean. Let cool in the pan for 10 minutes; remove from the pan, and let cool slightly on a wire rack.
Split the warm cake in half horizontally to make 2 layers. Place one layer, cut side up, on a cake plate; spoon half of the peaches over the layer. Place the remaining cake layer, cut side down, on top of the peaches. Spoon the remaining peaches on top of the cake.
Combine the sour cream and 1/2 cup of brown sugar in a small bowl; stir until smooth. Serve the sour cream mixture with the cake.