Millionaire’s Shortbread (aka Twix squares)

https://sugarspunrun.com/millionaires-shortbread/

Ingredients

Shortbread Crust

• 1 cup unsalted butter, softened 226g
• 1/3 cup sugar 70g
• 1/3 cup light brown sugar, packed 70g
• 1 large egg yolk
• 3/4 teaspoon vanilla extract
• 1/2 teaspoon salt
• 2 1/4 cups all-purpose flour 260g

Caramel

• 2 14-oz cans sweetened condensed milk 825ml
• 14 Tablespoons butter cut into Tablespoon-sized pieces (198g)
• 1 cup light brown sugar packed (200g)
• 1/3 cup light corn syrup 80ml
• 1 teaspoon vanilla extract
• 1/4 teaspoon salt

Chocolate Ganache

• 2 cups semisweet chocolate chips 340g
• 1/2 cup heavy cream 120ml
• 1/2 teaspoon vanilla extract 5ml
• sea salt for sprinkling

Instructions

• Preheat oven to 350F (177C) and line a 13x9 baking pan with parchment paper.
• Using an electric mixer, beat butter until well creamed.
• Add sugars and beat until light and fluffy, about 30 seconds.
• Add egg yolk and vanilla extract and stir well, pausing to scrape down the sides and mixing until ingredients are well-combined.
• Add flour, gradually (about 1/2 cup at a time), pausing to scrape down sides of bowl. Halfway through the addition of the flour, sprinkle in the salt with the beater still running.
• Don't over-beat the dough, you want it to be slightly crumbly to make it easier to press into the pan.
• Drop dough over prepared pan and gently, firmly, evenly, press dough into the bottom of the pan.  To make it easier, I usually lay a piece of wax paper over the dough and use the palm of my hand to smooth the surface (and then discard wax paper).
• Bake on 350F (177C) for 20-25 minutes -- edges should be lightly golden brown.
• Allow to cool while you prepare your caramel topping.

Caramel

• Combine condensed milk, butter, brown sugar, and corn syrup in a medium-sized saucepan over medium heat.
• Stir frequently until butter is melted and ingredients are well-combined. Continue to stir constantly until mixture begins to boil (this could take several minutes, but you don't need to increase the heat).
• Once mixture comes to a boil, reduce heat to a simmer (slowly bubbling), still stirring constantly.  Continue to stir 10-15 minutes until mixture turns a rich caramel color and has thickened (should begin pulling away from the sides of the pot as you stir).
• Remove from heat and immediately stir in the vanilla extract and salt.
• Pour evenly over prepared shortbread, use a knife to spread evenly if needed.
• Allow to cool at room temperature for several hours or in the refrigerator for 1 hour before topping with chocolate.

Chocolate Topping

• Combine chocolate chips and heavy cream in a small saucepan over medium heat.  
• Stir frequently until chocolate is melted and mixture is smooth.  
• Remove from heat and stir in vanilla extract.  Allow chocolate to cool just slightly for about 5 minutes, and then evenly spread over prepared caramel layer.  Wait several minutes and then sprinkle with sea salt.  
• Allow chocolate to harden (I recommend placing in refrigerator for about 30 minutes -- my family prefers these treats refrigerated anyway) before cutting and serving.