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

Set the prepared pan aside while you make the batter components.

In a small bowl, combine the packed brown sugar, ground cinnamon, melted butter, vanilla extract, and pinch of salt. Stir until the mixture looks like wet sand.

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

In a large mixing bowl, beat the butter and sugar together until pale and fluffy.

Add the eggs one at a time, mixing well after each addition.

Mix in the vanilla extract and sour cream until smooth.

Gradually add the flour mixture and milk alternately until just combined.

Spoon or pipe enough batter into each cupcake liner to fill it about one third full.

Add a small mound of cinnamon filling in the center of the batter.

Cover the filling with more batter until each liner is about two thirds full and swirl gently with a toothpick.

Bake for 18–22 minutes, rotating halfway through. Allow to cool in the tin for 5 minutes before transferring to a wire rack.

Beat the softened cream cheese until smooth, then add butter and mix until fluffy.

Gradually add powdered sugar and mix until well combined. Adjust consistency with cream.

Pipe the frosting onto each cool cupcake and finish with a light dusting of ground cinnamon.