Preheat oven to 200 degrees. In large bowl sift together flour, sugar, salt, baking soda and baking powder. In separate bowl whisk together egg, buttermilk, milk and melted butter. Slowly combine the dry ingredients with the wet ingredients. Stir until the flour disappears, but being careful not to overbeat the batter. In a large cast-iron skillet, melt about 1/2 tablespoon remaining butter. Ladle about 1/4 cup of batter into the pan for each pancake. Immediately press 4 or 5 banana slices into each so the batter oozes slightly over the fruit. Cook until bubbles appear and then flip and cook on the other side, about 3 minutes total. Transfer the pancakes to a platter and keep warm in the oven while you cook the remaining batches, adding butter to the pan as needed. Serve hot with syrup.