Preheat the oven to 350°F and lightly spray a 9-inch springform pan, lining the bottom with parchment paper.
Whisk flour, cocoa powder, baking powder, and salt in one bowl. In another, beat eggs, sugar, butter, and vanilla until fluffy.
Mix in the dry ingredients just until combined. Spread the batter into the pan and bake for 12 minutes, it should look slightly underbaked for that fudgy texture.
Heat heavy cream and chocolate chips in 20-second bursts, stirring until smooth.
Let cool. Beat cream cheese until creamy, then add sugar and cocoa powder. Mix in eggs one at a time, then fold in the melted chocolate and vanilla until smooth.
Pour over the brownie crust, smooth the top, and bake for about 65–70 minutes until edges are set but the center slightly jiggles. Let cool at room temperature, then refrigerate for at least 4 hours or overnight.
Top with whipped cream or chocolate garnish before serving. Use a warm, clean knife for perfect slices.