Preheat oven to 375°F. Line a 12-cup muffin tin with liners and lightly mist with spray.
Stir topping sugar and cinnamon together in a small bowl; set aside.
Whisk flour, baking powder, baking soda, salt, cinnamon, and nutmeg in a large bowl.
Whisk melted butter and oil with the granulated and brown sugars until glossy and combined.
Whisk in beaten eggs, vanilla, sour cream, and milk until the mixture looks smooth.
Fold wet ingredients into dry just until no dry streaks remain. Do not overmix.
Scoop batter into cups, filling each about three-quarters full.
Bake 16–19 minutes, until tops spring back and a tester comes out clean.
Cool 5 minutes. Brush warm tops with melted butter, then sprinkle generously with cinnamon sugar. Cool on a rack.