Preheat the oven to 175℃/350℉.
In a large bowl, add the melted butter and sugar together and mix using an electric whisk, regular whisk or wooden spatula, mix for about 2 minutes or until the sugar has dissolved a bit.
Add in the eggs and mix until well combined.
Add the vanilla essence and peppermint essence, if using. Mix until combined. Note: you don't want to overpower the blondies with peppermint crisp flavour by using both the peppermint crisp essence AND the peppermint flavoured caramel treat/dulce de leche. I only used the peppermint caramel treat.
Add the flour, corn starch, baking powder, and salt and mix until combined. Do not overmix but ensure there aren't any flour pockets left.
Scoop 1 cup worth of batter into a separate bowl and add the cocoa powder. Mix until well combined. Now it's time to assemble this guy.
In a 21cmx 21cm baking tin, add a layer of the blondie batter to the base of the tray. Gentle spread as much as possible, about 1cm thickness. Add tbsp sized dollops of the blondie batter on top, followed by the chocolate batter, followed by half of the caramel treat/dulce de leche and half of the peppermint crisp chocolate bar. Repeat once more, making sure you lightly smooth out the top prior to finishing it off with the remaining peppermint crisp bar. Note: pop the caramel treat/dulce de leche in a bowl and in the microwave for 30 seconds, it'll be easier to work with.
Bake for 1 hour. The edges should be dark brown in colour and pulling away from the baking tin. Allow to cool in the baking tin for a minimum of 1 hour before digging in. Cut into 9 equal squares and enjoy as is or with a scoop of vanilla ice cream. Lekker vreet, tastebud!