- Preheat to 375°F. Coat 11- x 7-inch baking pan with cooking spray.
- Heat 1 Tbs. butter in medium skillet over low heat. Add collard greens. Season with salt, if desired. Cover pan, and cook 4 minutes, or until tender, stirring occasionally. Transfer to plate to cool.
- Whisk together mashed sweet potato, eggs, and buttermilk in large bowl. Whisk in remaining 5 Tbs. butter. Fold in collard greens.
- Whisk together cornmeal, flour, sugar, baking powder, and salt in separate bowl. Fold dry ingredients into wet ingredients. (Do not overmix.) Spread batter in prepared pan.
- Bake 25 minutes, or until toothpick inserted into center comes out clean. Cool in pan on rack at least 10 minutes. Cut into 12 pieces. Serve warm or at room temperature.