Preheat oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper.
Whisk melted butter and sugar until smooth.
Add eggs, vanilla, and espresso powder and whisk until glossy.
Stir in cocoa powder, flour, and salt until just combined.
Spread brownie batter evenly into prepared pan.
In another bowl, beat cream cheese and sugar until smooth.
Add egg, dissolved espresso, and vanilla and mix until creamy.
Pour cheesecake mixture over brownie layer.
Swirl gently with a knife to create marble effect.
Bake 30–35 minutes until center is set.
Cool completely before slicing.