Preheat oven to 350 F. Line 12-count muffin pan with cupcake liners and set aside.
In medium bowl, whisk flour, baking powder, salt, cinnamon and nutmeg.
In large bowl, whisk butter and brown sugar 2 minutes, or until well combined. Add vanilla and egg; whisk until incorporated.
Add flour mixture to large bowl of wet ingredients. Stir until just combined; be careful to not overmix.
Fold in diced apples.
Spoon batter evenly into cupcake liners.
Bake 18-22 minutes, or until toothpick inserted into center of cupcake comes out clean. Let cool and serve.