To make crust:

Preheat to 350 degrees.

Butter or spray 12 x 8 or 14 x 4 rectangle fluted tart pan with nonstick cooking spray. May use 8 x 8 baking pan.

Stir together flour, brown sugar, and cornstarch. Add butter and cut into mixture until coarse crumbs forms. May use a food processor. Stir in water, starting with 1 Tablespoon and add more as needed, up to 2 Tablespoons. Add egg yolk and mix until it begins to come together.

Press dough on the bottom of the pan. Pierce bottom with a fork. Bake until lightly golden brown -- 18-22 minutes.

To make caramel: whisk sweetened condensed milk, brown sugar, butter, dark corn syrup, and vanilla in medium saucepan and cook over medium heat. Attach a candy thermometer to side of a pan. Bring to a gentle boil and keep cooking (8-10 minutes) or until caramel is pale golden and thick and temperature registers 225 degrees. Whisk constantly.

Once the caramel is thick, pour evenly over crust. Let set for 15 minutes.

To make chocolate ganache: melt chocolate and heavy cream in a microwave-safe bowl in 20-30 second increments until melted and smooth.

Pour chocolate over caramel. Sprinkle with sea salt flakes.

Chill in the refrigerator for at least 1 hour.

Cut into slices.

Recipe adapted from Bon Appetit Desserts Cookbook