Melt the butter in a medium heavy-bottomed saucepan (not non-stick) over medium heat.

Add heavy cream, brown sugar and salt and stir constantly over medium heat until combined. Bring to a boil and let boil for 4 minutes.

Remove from heat and stir in vanilla extract until combined. Transfer to a heat-proof container to cool completely at room temperature. Once the container is no longer hot to the touch, set aside ¼ cup (you'll be using this for the blondies), cover the rest and store in the fridge. Use it as a topping for ice cream later!

In a medium bowl, whisk to combine flour, baking powder and salt. Set aside.

In the bowl of a stand mixer, combine melted butter and brown sugar and beat on medium speed until combined.

Add egg and vanilla and beat to combine.

Add dry ingredients to the bowl of wet ingredients and mix on low speed until completely combined. As the batter thickens, you may need to turn it up to a higher speed.

Add chocolate chunks (save a handful for topping) and stir until just combined.

In your prepared baking dish, spread batter in an even layer.

Drizzle your prepared butterscotch sauce over the top of the batter and gently swirl with a knife (see notes for more details). Press your reserved chocolate chunks into the top and top with flake salt (if desired).

Bake for 20 minutes, or until a toothpick inserted into the center (try to aim for a non-butterscotch sauce spot) comes out mostly clean. Let cool in pan for 10 minutes, then left them out of the pan with the parchment paper and transfer to a wire rack to cool completely.

Cut into 12-16 bars, serve and enjoy!