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.
Video
Notes
Brownie mix: Use a regular box, about 18 ounces.
Water: Substitute the same amount of milk, buttermilk, or cooled brewed coffee.
Instant coffee: Optional. Skip if using brewed coffee.
Cream cheese: Use softened block cream cheese to avoid lumps.
Egg: Use 1 egg for the cheesecake, plus the eggs listed on the brownie mix box.