Preheat the oven to 350°F and grease your muffin pan. You can do this by rubbing some butter on all of the tins.
With an electric mixer, beat together the butter and sugar on medium speed until creamy, light and fluffy. Add the egg and beat together until smooth.
In a bowl, stir together the flour, baking soda, baking powder, salt, nutmeg and cinnamon with a spoon. Add the dry ingredients to the butter mixture in two increments, alternating with the buttermilk and vanilla. Stir until just evenly combined. There might be a few lumps.
Spoon the batter into each muffin tin, filling it about three-fourths full. Be sure to fill unused muffin cups with a bit of water to prevent warping in the oven. Bake until golden and springy, about 20-25 minutes. Let cool for 15 or so minutes.
To make the topping, stir together the sugar and the cinnamon in a small bowl. Then, melt the butter in another bowl. When the muffins are cool enough to work with, brush a layer of melted butter onto each muffin, followed with a generous sprinkling of the cinnamon sugar. Enjoy warm!