For the muffins:
- 1 3/4 cups (220 g) all-purpose flour
- 1 teaspoon baking powder
- 1/2 teaspoon baking soda
- 1/2 teaspoon salt
- 1 teaspoon ground cinnamon
- 1/4 teaspoon ground nutmeg (optional)
- 1/2 cup (115 g) unsalted butter, melted and slightly cooled
- 1/2 cup (100 g) granulated sugar
- 1/4 cup (55 g) brown sugar, packed
- 2 large eggs
- 1/2 cup (120 ml) whole milk
- 1 teaspoon vanilla extract
- 1 1/2 cups (180 g) peeled and finely diced apples (about 2 medium apples)
For the crumb topping:
- 1/2 cup (65 g) all-purpose flour
- 1/3 cup (65 g) brown sugar, packed
- 1 teaspoon ground cinnamon
- 1/4 cup (60 g) unsalted butter, melted
For the glaze (optional):
- 1/2 cup (60 g) powdered sugar
- 1–2 tablespoons milk or heavy cream
- 1/4 teaspoon vanilla extract