In a large bowl, stir together cornmeal, flour, soda cumin, salt and pepper Using large holdes on a shredder, shred zucchini to make 3/4 cup (packed). Squeeze with your hands to extract excess moisture. In a medium-size bowl, mix egg, buttermilk, oil, zucchini, corn and green onion. Pour liquid into dry ingredients and stir until evenly moistened. Heat a large skillet or griddle over medium-high heat. Grease lightly with butter. Spoon about 2 tablespoons bater onto skillet for each cake, spreading batter to make 3-inch cakes. Cook until tiny bbbles form in the centers and edges of cakes appear dry; turn and cook other sides until browned and cakes puff slightly. Serve 2 or 3 cakes per person. Top each serving with sour cream as desired.