Preheat oven to 350F, line a 9x13-inch pan with aluminum foil for easier cleanup, and spray with cooking spray; set aside.

To a large bowl, add the flour, brown sugar, and whisk to combine.

Add the 1/2 cup diced butter and cut the butter in with a fork until you have small crumbly bits.

Transfer mixture to prepared pan, hard pack it with a spatula or the palm of your hand, and bake for about 6 to 8 minutes, or until barely golden browned.

While the crust bakes, to a medium saucepan add the butterscotch chips, corn syrup, 2 tablespoons butter, and heat over medium heat to melt. Stir nearly continuously. The butterscotch chips may be a bit resistant to melting, but just keep stirring to encourage them to melt. Stirring is important so the corn syrup doesn't burn.

After the crust is done baking, evenly sprinkle the peanuts, evenly drizzle the butterscotch sauce mixture, and evenly sprinkle the chocolate chips.

Return pan to oven and bake for about 8 to 10 minutes, or until the butterscotch sauce is lightly bubbling and likely the chocolate chips will have softened and spread a bit but not completely melted into puddles.

Remove pan from oven and allow to cool for about 2 hours on a wire rack, or until bars have set up completely. Immediately upon pulling the pan from the oven, it will be very soupy looking on top and not at all set, but in time it will set completely.