Servings: 32

1 cup salted butter, softened 1 cup salted butter, softened
1 cup packed brown sugar, divided 1 cup packed brown sugar, divided
1/3 cup granulated sugar ⅓ cup granulated sugar
1 large egg yolk 1 large egg yolk
2 teaspoons vanilla, divided 2 teaspoons vanilla, divided
1/2 teaspoon salt ½ teaspoon salt
2 cups all purpose flour 2 cups all purpose flour
1/2 cup salted butter, cut into pieces ½ cup salted butter, cut into pieces
1 14- ounce can sweetened condensed milk 1 14- ounce can sweetened condensed milk
1/2 cup heavy cream ½ cup heavy cream
1 12- ounce package semisweet chocolate chips 1 12- ounce package semisweet chocolate chips
Flaky sea salt Flaky sea salt

Make Dough: subheading: 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 ⅓ 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 Into Pan: subheading: Press Into Pan:
Press evenly into bottom of prepared baking pan.
Bake: subheading: Bake:
Bake until edges are golden and center is set, 18 to 22 minutes. Cool in pan on a wire rack.
Make Caramel: subheading: Make Caramel:
Meanwhile, in a medium saucepan combine the ½ cup butter pieces and remaining ⅔ 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: subheading: Spread Caramel:
Spread caramel mixture evenly over crust. Cover and chill until set, about 30 to 40 minutes.
Melt Chocolate: subheading: 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: subheading: 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: subheading: Cut and Serve:
Using edges of parchment paper, lift out shortbread. Cut into bars.
How to Store Millionaire Bars: subheading: How to Store Millionaire Bars:
Place the million dollar bars in a single layer in an airtight container and cover. Store in the refrigerator up to 1 week or freeze up to 3 months.