Chocolate Caramel Millionaire Bars Recipe

Make Dough
Preheat oven to 350°F. Line a 13x9x2-inch baking pan with parchment paper, extending paper over edges. In the large bowl of an electric mixer, beat 1 cup softened butter on medium speed until creamy, about 30 seconds. Add 1/3 cup of the brown sugar and the granulated sugar and beat until light and fluffy, about 1 to 2 minutes. Beat in egg yolk, 1 teaspoon of the vanilla, and salt until combined. Gradually mix in flour on low speed just until combined and mixture is crumbly.
Press evenly into bottom of prepared baking pan.

Bake
Bake until edges are golden and center is set, 18 to 22 minutes. Cool in pan on a wire rack.

Make Caramel
Meanwhile, in a medium saucepan combine the 1/2 cup butter pieces and remaining 2/3 cup brown sugar. Cook over medium-high heat until butter is melted, stirring constantly, about 2 to 3 minutes. Add in sweetened condensed milk. Bring to a gentle boil, stirring constantly. Reduce heat to low and simmer until golden, stirring frequently, about 12 to 14 minutes. Remove from heat. Stir in remaining 1 teaspoon vanilla.

Spread Caramel
Spread caramel mixture evenly over crust. Cover and chill until set, about 30 to 40 minutes.

Melt Chocolate
In a small saucepan heat heavy cream over medium heat until just simmering, about 3 to 4 minutes. Remove from heat. Add chocolate chips and let stand 5 minutes. Stir until smooth.

Spread Chocolate
Evenly spread chocolate layer over caramel layer. Sprinkle with flaky sea salt. Cover and chill until set, about 1 hour.

Cut and Serve
Using edges of parchment paper, lift out shortbread. Cut into bars.