Preheat the oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper and lightly spray the parchment and any exposed pan with nonstick spray; set aside.
Make the brownie batter: melt the butter and chopped semisweet chocolate together in a small saucepan over medium-low heat, whisking occasionally until smooth. Remove from heat and transfer to a large heatproof bowl.
Whisk the brownie sugar into the melted chocolate until combined. Add the 2 large eggs and 1 extra egg yolk and whisk until smooth.
Gently whisk in the salt and the flour just until combined. Spread the brownie batter evenly in the prepared pan and smooth the top with a spatula.
Make the cheesecake layer: using a handheld mixer or electric mixer, beat the softened cream cheese until completely smooth. Add the 1/2 cup sugar, 1 large egg, and 1 extra egg yolk and beat until creamy, about 1 minute.
Fold most of the chopped Butterfinger pieces into the cheesecake batter, reserving about 1/4 cup crumble for topping.
Pour the cheesecake batter over the brownie layer. Using a knife, swirl gently through the batters to create a marbled effect.
Bake in the preheated oven for 35 minutes, or until the edges are set and the center is just set but not liquid. Remove from oven and cool completely in the pan on a wire rack.
Make the peanut butter glaze: place the peanut butter in a small saucepan over medium-low heat and warm until melted and smooth, stirring occasionally. Whisk in the confectioners' sugar until combined and smooth.
Lift the cooled bars from the pan using the parchment. Cut into squares, sprinkle each with the reserved Butterfinger crumble, and drizzle with the peanut butter glaze before serving.