1/4 cup vegetable oil
1 large egg, at room temperature
1 teaspoon vanilla extract
1/2 cup granulated sugar
1 cup all-purpose flour
1/2 teaspoon baking soda
1/4 teaspoon kosher salt
1/2 teaspoon ground cinnamon
1/4 teaspoon freshly grated nutmeg
Prepare the Muffins: Preheat oven to 350°F. Lightly grease a 24-cup miniature muffin pan with cooking spray. Stir together sour cream, oil, egg, vanilla, and 1/2 cup sugar in a small bowl. Whisk together flour, baking soda, salt, 1/2 teaspoon cinnamon, and 1/4 teaspoon nutmeg in a medium bowl. Whisk sour cream mixture into flour mixture. (Batter will be very thick.) Spoon 1 tablespoon of batter into each prepared muffin cup, keeping batter rounded on top
Bake in preheated oven until golden and springy when touched lightly on top, 10 to 12 minutes. Cool in pan 5 minutes. Remove from pan to a wire rack; cool completely, about 15 minutes.
Prepare the Coating: Place melted butter in a small bowl. Whisk together 1 cup sugar, 1 1/2 teaspoons cinnamon, and 1/2 teaspoon nutmeg in another small bowl.
Dip 1 Muffin in butter; immediately dredge in sugar mixture, and place on a serving platter. Repeat with remaining Muffins, butter, and sugar mixture.