Cooking spray
2 cups semisweet chopped chocolate or chocolate chips
1/2 cup butter
3/4 cup light brown sugar
3/4 cup granulated white sugar
4 large eggs
2 teaspoons vanilla extract
1 cup all-purpose flour
1/2 teaspoon kosher salt
12 regular size Reese's Peanut Butter Cups
Preheat the oven to 325 F. Line a 9-inch-square baking dish with aluminum foil, and spray the foil with cooking spray.
In a large, microwave-safe mixing bowl, combine the chocolate and butter. Microwave on 50% power in 30-second intervals, stirring in-between until the chocolate is completely melted and the mixture is smooth.
Whisk the white and brown sugars into the chocolate to incorporate. Add the eggs, one at a time, while whisking constantly, until the mixture is smooth and well-combined. Add the vanilla, flour and salt, and stir to mix well.
Transfer half the batter to the prepared baking pan, and spread it out into an even layer with a rubber spatula.
Arrange the peanut butter cups in a single layer, cutting them as needed, on top of the batter. Pour the remaining batter over the top, covering the peanut butter cups completely. Smooth with a spatula.
Bake for about 30 minutes until the top is set.
Remove the pan from the oven. Set on a wire rack to cool completely.
To serve, cut into squares.
