Pour into parchment-lined 7" square (or similarly sized) baking pan (unless using silicone, then no parchment). Reserve a few spoonfuls of batter to make the fudge swirl (optional). Set aside.
Mix cheesecake ingredients until well combined.
Pour cheesecake batter over brownie batter.
Spoon remaining brownie batter on top, and swirl with the back of a knife.
Bake for 25 minutes, and check to see if firm. If not, check every 1 -2 minutes and remove from oven when firm. Do not overbake.
Let cool, and enjoy! Store in the refrigerator.
Notes
A note about substitutions: because each type of protein powder has a distinct flavor and texture when baked, I would not try substituting different types of protein powders in this recipe. (See my Recipe Basics video for examples of what goes wrong when you use the wrong protein powder.)