In a bowl, beat cream cheese, sugar, salt, and vanilla on medium-low speed until smooth. Add egg and mix just until combined. Set aside.
Prepare brownie batter according to package directions. Spread evenly in a 9×9-inch pan.
Spoon dollops of cheesecake mixture over brownie batter. Use a knife or chopstick to gently swirl.
Bake according to package directions, adding a few extra minutes if needed. Cheesecake layer should look set and not wet in the center. A toothpick in the brownie part should have a few moist crumbs.
Let cool, then chill in the fridge for at least 1 hour before cutting.
Notes
Brownie mix: Any brand works. Follow package directions.
Water: Swap with milk, buttermilk, or brewed coffee for richer brownies.
Instant coffee: Optional, but brings out the chocolate flavor and keeps brownies from tasting too sweet.
Cream cheese: Let it sit out about 30 minutes so it softens and mixes smoothly.
StorageStore brownies covered in the refrigerator for up to 5 days. Let them sit at room temperature for a few minutes before serving.Tips for Best Brownies
Let cream cheese soften first so it mixes smoothly.
Line pan with parchment so brownies don't stick.
Don’t overbake — start checking a few minutes early.