Prep Oven: Preheat to 350°F. Line an 8-inch square baking pan with foil, leaving overhang. Lightly grease or spray with cooking spray.
Make Brownie Base: In a large microwave-safe bowl, melt butter and chocolate together in 30-second bursts. Stir smooth. Let cool slightly.
Add Sugar and Eggs: Whisk in sugar, vanilla, optional coffee, and espresso powder. Beat in eggs until glossy.
Finish Batter: Stir in flour and salt just until combined. Spread batter evenly in pan.
Mix Cheesecake Layer: In another bowl, beat cream cheese, egg, and sugar until smooth. Stir in white chocolate chips.
Assemble Layers: Drop cheesecake mixture by large spoonfuls over brownie batter. Gently swirl with a knife or spatula to create a marbled effect.
Add Toppings: Scatter chopped Oreos and semisweet chocolate chips on top.
Bake: Bake for 43–45 minutes until edges are set and center is just slightly jiggly. Cool completely on a wire rack.
Chill: Cover and refrigerate for at least 3–4 hours (preferably overnight) before slicing.