Step 1

Preheat oven to 375 degrees. Line a 10-cup standard muffin tin with paper liners; set aside. Combine 2 tablespoons sugar and 1/4 teaspoon cinnamon in a small bowl; set aside. In a large bowl, whisk together the flour, baking powder, salt, nutmeg, and remaining 3/4 cup sugar and 1/2 teaspoon cinnamon; set aside.

Step 2

In another large bowl, whisk together eggs, vanilla, and milk. Whisk in the melted butter. Using a rubber spatula, fold the egg mixture into the flour mixture until just combined. Dividing evenly, fill each of the 10 muffin cups halfway with batter.

Step 3

Distribute the plum pieces evenly among the cups (about 3 tablespoons per muffin), scattering them over the batter. Spoon the remaining batter on top, dividing evenly. Sprinkle tops with the reserved cinnamon-sugar mixture.

Step 4

Bake, rotating the pan halfway through, until the muffins are puffed and golden brown and a cake tester inserted in the center of one muffin comes out clean, 15 to 17 minutes. Transfer the pan to a wire rack and let stand 5 to 10 minutes. Turn out the muffins onto the rack to cool a few minutes. Serve warm.