Preheat the oven to 350F /180?c / Gasmark 5. In a large bowl combine the flour, sugars, nutmeg, baking powder, baking soda, salt, and just leave to one side. Place the egg, mashed bananas, melted butter and vanilla and in a mixing bowl and mix well together. With a wooden spoon, lightly fold the wet ingredients (banana mixture) into the dry ingredients until just combined and batter is thick and chunky. (The essential thing is not to over mix the batter, its not supposed to be smooth and over mixing the batter will make tough, rubbery muffins. Line a muffin tray with paper muffin cases, and then fill each case to just below the top with the muffin mixture you can top this with a slice of banana. Bake the muffins for 20-25 minutes. They are cooked when a skewer inserted into one and then removed comes out clean. Let cool slightly and enjoy!