Make the chocolate chip shortbread layer: Preheat the oven to 350 F. Line the bottom of an 8” square pan with parchment paper. With a hand mixer, beat together the butter, brown sugar, salt and vanilla until fluffy. Add the powdered sugar and flour and beat to just combine. Fold in the chocolate chips. Press the dough into the pan in a a flat layer. Bake for 20 minutes, until golden brown on the edges.
While the shortbread bakes, make the caramel: combine sweetened condensed milk, butter and syrup into a pot. Cook on low medium heat, stirring constantly so as not to scorch the milk. Once the temperature reaches 220-225 F is thick and the color of butterscotch, turn off the heat and add the sea salt and vanilla. Stir to combine.
If the shortbread still hasn’t finished baking, keep the caramel over very low heat, to just keep it warm. Once the shortbread is done, remove from the oven and pour the caramel over it. Smooth into one even layer. Set aside to cool completely.
From each bowl of chocolate, set aside 1/4 of the amount to be your ‘seed’. Melt the chocolate(s) in the microwave in 30 second increments, Stirring between, until the chocolate is mostly melted but not fully. Add the seed you’ve set aside and stir until chocolate is smooth. Pour the dark chocolate over the now cool caramel and smooth into one layer. If you are using white and milk, alternate spooning them over the dark chocolate. Use a butter knife to swirl them. Top with edible glitter if desired.