Preheat oven to 350°F (176°C). Line a 12-cup muffin tin with paper liners.

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the sour cream and vanilla extract until well combined.

Add the egg whites one at a time, beating well after each addition.

In a separate bowl, whisk together the flour, baking powder, and salt.

In a small bowl or liquid measuring cup, whisk together the apple butter and milk.

Add half of the dry ingredients to the wet ingredients and mix until just combined. Add the apple butter mixture and mix until combined. Add the remaining dry ingredients and mix until just combined. Be careful not to overmix.

In a small bowl, combine the cinnamon and 0.25 cup of sugar for the swirl.

Fill each cupcake liner about halfway with batter. Sprinkle some of the cinnamon-sugar mixture over the batter. Top with a little more batter, filling the liners about two-thirds full. Sprinkle with remaining cinnamon-sugar.

Bake for 17-19 minutes, or until a toothpick inserted into the center comes out clean.

Let cupcakes cool in the tin for a few minutes before transferring them to a wire rack to cool completely.

In a large bowl, beat together the softened butter and cream cheese until smooth and creamy.

Gradually add the powdered sugar and cinnamon, mixing until well combined.

Add the milk, one tablespoon at a time, until the frosting reaches your desired consistency.

Once the cupcakes are completely cooled, frost them generously with the cinnamon cream cheese frosting.

Optionally, sprinkle with a little extra cinnamon sugar or top with a small apple chip.