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

In a bowl, mix the melted butter and sugar until well combined.

Add in the eggs, one at a time, then stir in the vanilla extract.

Sift together the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Spoon the brownie batter into the bottom of each cupcake liner, filling them about halfway.

Place the muffin tin in the preheated oven and bake for about 10-12 minutes, or until the edges are firm but the center is still a little soft.

Remove them from the oven and let cool slightly.

In a mixing bowl, beat the softened cream cheese until smooth and creamy.

Gradually add in the sugar, mixing well.

Beat in the eggs one by one, then mix in the vanilla extract and sour cream until smooth and well blended.

Pour the cheesecake filling over the brownie base in each cupcake liner, filling them just about to the top.

Return the tin to the oven and bake for an additional 15-18 minutes, or until the cheesecake is set but slightly jiggly in the center.

Remove the mini cheesecakes from the oven and let them cool to room temperature.

Transfer them to the refrigerator for at least 2 hours to allow them to set properly.

Once chilled, remove the mini cheesecakes from the liners and serve them as is or topped with your favorite treats.