For the Muffins:
7 tablespoons unsalted butter, at room temperature
⅔ cup sugar
1 egg
1-1/2 cups all-purpose flour
1-1/2 teaspoon baking powder
½ teaspoon baking soda
½ teaspoon salt
½ teaspoon nutmeg
½ cup buttermilk**
1-1/2 teaspoon vanilla extract
**If I'm out of buttermilk, I like to substitute 1/4 cup whole milk + 1/4 cup sour cream, which I whisk together until incorporated and then add to the recipe as directed.
For the Topping***:
⅔ cup sugar
1 tablespoon ground cinnamon
6 tablespoons unsalted butter, melted
For the Topping***:
⅔ cup sugar
1 tablespoon ground cinnamon
6 tablespoons unsalted butter, melted
***This makes way more than you need, but is what the original recipe calls for. I find that 1-1/2 teaspoons cinnamon + 1/3 cup sugar is plenty. You won't use it all.
Preheat an oven to 350 degrees. Grease 9 standard muffin cups with butter or non-stick cooking spray; fill the unused cups one-third full with water to prevent warping.
To make the muffins, in the bowl of an electric mixer fitted with the flat beater, combine the butter and sugar and beat on medium speed until light and fluffy. Add the egg and beat well until pale and smooth.
In another bowl, stir together the flour, baking powder, baking soda, salt, and nutmeg. Add to the butter mixture in 2 additions, alternating with the buttermilk and vanilla. Stir just until evenly moistened. The batter will be slightly lumpy.
Spoon the batter into the prepared muffin cups, filling each three-fourths full. Bake until the muffins are golden, dry and springy to the tough and a toothpick inserted into the center of a muffin comes out clean, about 20 minutes. (May take up to 30 minutes to bake if you have more than 9 muffins in your tin or if your muffins are larger in size). Transfer the pan to a wire rack and let cool for 5 minutes. Unmold the muffins and let stand until cool enough to handle.
To make the topping, in a small, shallow bowl, stir together the sugar and cinnamon. Put the melted butter in another small bowl. Holding the bottom of a muffin, dip the top into the melted butter, turning to coat it evenly. Immediately dip the top in the cinnamon-sugar mixture, coating it evenly, then tap it to remove excess sugar. (Alternatively, you can use a pastry brush to brush melted butter on top of the muffins and then sprinkle the cinnamon-sugar mixture over each muffin with a spoon).
Transfer the muffin, right side up, to the rack. Repeat with the remaining muffins. Let cool completely before serving. Makes 9 muffins.