Step 1

Start with the shortbread: Preheat the oven to 350ºF and line an 8x8-inch baking pan with parchment paper with about 1 inch of overhang on the sides. Set aside.

Step 2

In the bowl of a stand mixer, or a large mixing bowl with a hand mixer fitted with the paddle attachment, cream together the butter, granulated sugar and powdered sugar on medium speed until smooth and fluffy. Scrape down the bottom and sides as needed. Add the egg yolk and vanilla, beating together for 1 minute. With the mixer on low, add the flour and salt, and beat together until just combined. (Try to not overmix, just until all ingredients are combined).

Step 3

Press the shortbread dough into an even layer into the prepared baking pan. Using a fork, pierce the dough all over the top. Bake until the edges are lightly golden brown, about 25-28 minutes.

Step 4

While the shortbread finishes baking, make the caramel: In a small saucepan, or in the microwave, heat the cream, butter, and salt together over medium heat until the butter has melted. Set aside.

Step 5

In a separate medium saucepan, heat the sugar, corn syrup, and water together over medium heat until the sugar mixture begins to boil. Keep cooking until the bubbles get smaller and begin to turn amber-colored. Reduce the heat to low, and carefully pour in the warm butter/cream mixture, whisking constantly to avoid lumps or crystals.

Step 6

Add a candy thermometer to the side of the pot and simmer the caramel while continuously whisking until it reaches 245ºF. Remove from the heat and stir in the vanilla.

Step 7

Carefully pour the hot caramel over the shortbread crust. Place in the refrigerator for about 1 hour before adding the chocolate ganache topping.

Step 8

Make the chocolate ganache: In a small saucepan over a double boiler, or in the microwave, add the cream and chocolate. Cook over medium-low heat, stirring frequently, until the chocolate has melted and is smooth.

Step 9

Remove from the heat and carefully pour over the cooled caramel layer. Gently smooth it over the top in an even layer using an offset spatula. Allow the ganache to set in the refrigerator for 30 minutes. If desired, before chilling, garnish with flaky sea salt.

Step 10

Leftovers stay fresh covered tightly at room temperature or in the refrigerator for up to 1 week.