To make the brownies, preheat oven to 325F. Grease or parchment-line a 9×13-inch metal pan. Set aside.
In a large saucepan, combine butter, sugars, and water.
⅔ cup butter, 1 cup granulated sugar, ½ cup brown sugar packed, ¼ cup water
Bring to a boil, stirring regularly.
Remove pan from heat.
Whisk in 1 ¾ cups chocolate chips until melted and well-combined.
2 ½ cups bittersweet chocolate chips
Add eggs and vanilla. Whisk until well-combined.
4 large eggs, 1 teaspoon vanilla extract
Add flour, salt, and baking soda. Whisk in just until combined. Don’t overmix.
1 ½ cups all-purpose flour, ½ teaspoon salt, ½ teaspoon baking soda
Stir in the remaining 3/4 cup chocolate chips. Set aside.
To make the cheesecake portion, beat the cream cheese and granulated sugar in a medium mixing bowl on medium speed until combined.
16 ounces cream cheese, ⅔ cup granulated sugar
Add the vanilla, salt, and eggs. Mix in until well-combined, scraping the bowl as needed.
1 teaspoon vanilla extract, ⅛ teaspoon salt, 2 large eggs
Reserve 1 cup brownie batter.
Pour the remaining batter into the prepared pan, smoothing as needed.
Spoon dollops of cheesecake batter over the brownie batter in the pan.
Drop dollops of the reserved brownie batter over the cheesecake batter. It doesn't need to cover the cheesecake batter.
Sprinkle the mini chocolate chips over the top.
1 tablespoon mini semisweet chocolate chips
Using a thin knife, lightly swirl the cheesecake and brownie batters. There are tips and photos above the recipe.
Bake for about 35-45 minutes, or until a toothpick inserted in the center comes out with a few fudgy crumbs.
Let the brownies cool to room temperature before cutting and serving.
Notes
Butter: I use salted butter in this recipe. If using unsalted butter, increase the salt to 3/4 teaspoon.
Brown sugar: I use light brown sugar in this recipe.
Chocolate chips: Bittersweet chocolate chips are 60% cacao. A good substitute would be dark chocolate chips. If you prefer, you can use semisweet chocolate chips. However, the brownies will be sweeter.
All-purpose flour: It’s important to use a light hand when measuring flour for brownies. To get the proper amount of flour, weigh the flour (click on "metric" just above the ingredients for the weights) or sift or stir the flour. Lightly spoon into the measuring cup and level.