Preheat Oven and Prepare Pan: Preheat oven to 350°F (175°C). Grease and line a 9-inch springform pan with parchment paper.
Brownie Batter: In a bowl, mix melted butter, sugar, cocoa powder, eggs, and flour until smooth. Spread half the batter in the pan. Bake for 10-12 minutes. Let cool slightly.
Cheesecake Layer: Beat cream cheese and sugar until smooth. Add eggs one at a time, then vanilla. Pour over brownie base.
Top with Brownie Swirl: Drop spoonfuls of remaining brownie batter on cheesecake layer and swirl gently.
Bake Cheesecake: Bake 35-40 minutes until set. Cool, then refrigerate 4 hours or overnight.