Preheat oven to 375 degrees. Coat 12 inch cast iron frying pan with unsalted butter.
Heat 1 tbsp butter in a skillet and add collard greens. Add a little salt for seasoning. Cook greens until tender about 6 minutes.
Whisk together mashed sweet potato, eggs, and buttermilk. Then add the remaining melted 5 tbsp of butter. Fold in collard greens.
In a separate bowl whisk together cornmeal, flour, sugar, baking powder, and salt.
Fold flour mixture into sweet potato mixture.
Pour the mixture into 12 inch cast iron frying pan. Spread evenly.
Bake for 25-30 minutes or until an inserted toothpick comes out clean.
Cool on rack and top with more butter.