Preheat your oven to 325°F (165°C). Prepare a muffin tin with liners and spray with non-stick spray.

In a bowl, whisk together melted butter and sugar. Beat in eggs and vanilla until smooth.

Combine cocoa powder, flour, and salt in a separate bowl. Fold dry mixture into wet mixture and mix in chocolate chips. Fill muffin cups a third full and bake for 10-12 minutes.

In a bowl, beat cream cheese until creamy. Mix in sugar and eggs one by one, then fold in sour cream and vanilla.

Pour cheesecake mixture over brownie bases. Top with mini chocolate chips if desired. Bake in a water bath for 20-25 minutes.

Turn off oven and crack door open; cool cups for 30 minutes. Transfer to wire rack; refrigerate for at least 4 hours.