Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with colorful cupcake liners.

In a medium bowl, combine the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt. Whisk thoroughly.

In a large bowl, cream together the softened unsalted butter and granulated sugar until light and fluffy, about 3-4 minutes.

Add the large eggs, one at a time, mixing well. Stir in the vanilla extract until fully combined.

Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream, mixing until just combined.

Pour in the whole milk and mix gently until the batter is smooth.

In a small bowl, mix the brown sugar and ground cinnamon for the swirl. Drizzle melted butter in, stirring to form a thick paste.

Scoop the batter into the lined muffin tin, filling each cup about two-thirds full. Add a dollop of the cinnamon-sugar swirl on top and swirl gently.

Bake for 18-22 minutes or until a toothpick comes out clean.

Cool in the tin for 5 minutes before transferring to a wire rack. Prepare the glaze and drizzle over the cooled cupcakes.