Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.

In a small bowl, combine the softened butter, light brown sugar, and ground cinnamon for the swirl. Mix with a fork or spatula until it forms a thick, smooth paste. Set aside.

In a medium bowl, whisk together the all-purpose flour, baking powder, and salt.

In a large bowl, beat the room temperature butter and granulated sugar with a stand mixer or hand mixer on medium-high speed until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, beating well after each. Then beat in the vanilla extract.

Add the dry ingredients in three parts, alternating with the milk in two parts, beginning and ending with dry ingredients. Mix on low speed until just combined.

Fill each cupcake liner about two-thirds full with batter.

Drop about 1 teaspoon of the cinnamon filling onto the center of each. Gently swirl in with a toothpick or knife to create a marbled effect.

Bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Cool in the tin for a few minutes, then transfer to a wire rack to cool completely.

For the frosting, beat the cream cheese and butter together until smooth. Gradually add powdered sugar, then vanilla. Add milk if needed for consistency.

Frost the cooled cupcakes generously. Sprinkle with extra cinnamon if desired.