Preheat oven to 350°F. Line a 12-count cupcake tin with paper liners. Set aside.
Add the butter to a small saucepan set over medium heat. Once the butter has melted, begin stirring constantly until the butter gets foamy, then begins to brown. This will take 5-8 minutes. Once browned, pour the butter into a small bowl and set aside to cool.
½ cup unsalted butter
In a medium bowl, whisk the flour, baking soda, baking powder, salt, and cinnamon together.
1½ cups all-purpose flour, 1 teaspoon baking soda, ¼ teaspoon baking powder, ½ teaspoon kosher salt, 1 teaspoon ground cinnamon
In a large bowl, whisk the browned and cooled butter, brown sugar, sugar, eggs, milk, and vanilla extract together.
½ cup brown sugar, ½ cup granulated sugar, 2 large eggs, ⅓ cup milk, 2 teaspoons pure vanilla extract
Add the dry ingredients to the wet and stir until just combined. Fold in the apples.
1 large apple
Fill the cupcake liners ¾ of the way full (you may need more than 12). Bake for 20-25 minutes or until a toothpick inserted into the center comes out with just a few moist crumbs.
Let cool in the pan for 3 minutes, then transfer to a wire rack to cool completely.