• Preheat your oven to 350°F.
• Grease and line an 8-inch square baking pan with nonstick aluminum foil, regular aluminum foil greased with cooking oil spray, or parchment paper. Set the pan aside.

Make the cheesecake mixture.

• In the bowl of a stand mixer fitted with the paddle attachment, or a large bowl with a handheld mixer, place the cream cheese, 1/8 teaspoon salt, 1 teaspoon vanilla, and 1/2 cup sugar, and beat until very smooth.
• Add the egg, and beat again until smooth.
• Transfer this mixture to a spouted 2 cup measuring cup, and set it aside.

Make the brownie base.

• In a the same mixing bowl, place the flour, xanthan gum, cocoa powder, baking powder, 1/2 teaspoon kosher salt and 1 cup sugar, and whisk to combine well.
• Add the melted butter, eggs, and vanilla, and beat until smooth.

Combine the batters.

• Transfer the brownie mixture to the prepared pan and spread it into an even layer.
• Pour the cheesecake mixture on top, and spread it into an even layer on top.
• Using a chopstick, butter knife, or other small tool, swirl the batters together gently in a zigzag pattern. The top will look mostly like it’s only cheesecake batter.
• Scatter the optional mini chocolate chips on top in an even layer.

Bake the brownies.

• Place the baking pan in the center of the preheated oven and bake, rotating once during baking, until the cheesecake layer jiggles but only in a controlled, not a loose, way and the top no longer glistens (about 40 minutes). It’s better to underbake than to overbake.
• Remove from the oven and allow to cool in the pan until no longer hot to the touch, at least 30 minutes.
• Place the pan in the refrigerator for 1 hour or until firm.
• Remove the brownies from pan, peel away the foil or parchment paper, and slice with a sharp, clean and wet knife into 9 equal pieces.