Preheat oven to 350 degrees Fahrenheit (175°C).

Line a 12-cup muffin pan with paper liners.

In a small bowl, mix the 0.5 cup packed light brown sugar and 1.5 teaspoons ground cinnamon together. Set aside for the topping.

In a large bowl or stand mixer, combine the 0.67 cup white sugar and 0.5 cup softened butter. Beat until smooth and creamy.

Add the 2 large eggs and 2 teaspoons vanilla extract to the sugar-butter mixture. Continue to beat on medium speed until well combined.

Gradually add the 1.5 cups all-purpose flour and 1.5 teaspoons baking powder to the wet ingredients, alternating with the 0.5 cup milk. Mix until just combined, being careful not to overmix.

Gently fold in half of the 1 large peeled and finely chopped apple into the muffin batter.

Fill each muffin liner halfway with the batter.

Cover the batter in each liner with the remaining chopped apples, pressing them lightly into the batter with the back of a spoon.

Sprinkle the reserved brown sugar and cinnamon mixture evenly over the top of each muffin. If desired, swirl the topping into the batter lightly with a butter knife.

Bake for 30 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Allow muffins to cool in the pan for 10 minutes before transferring them to a wire rack to cool completely.