1 1/2 cups (3 sticks) butter, divided
2 1/2 cups all-purpose flour, divided
1 1/4 cups sugar, divided
2 tbsp. cornstarch
1 (12 oz.) pkg. individually wrapped soft caramels
1/4 cup whole milk
1 (10 oz.) bar bittersweet or semi-sweet chocolate (finely chopped)
3 large eggs
1 tbsp. vanilla
1/2 tsp. baking powder
1/4 tsp. salt

Cut 1 cup (2 sticks) butter into chunks. In food processor combine 2 cups flour, 1/2 cup sugar, cornstarch and butter chunks. Whirl until dough. Press evenly over buttered 9x13-inch baking pan.

Bake in oven at 325°F until top feels dry and is just beginning to brown (about 25 minutes). Cool completely.

Unwrap caramels and place in microwave safe bowl with milk. Cook on full power for 1 minute. Stir, then cook and stir at 30 second intervals until melted and smooth, about 3 minutes longer. Spread caramel mixture evenly over cooled crust and chill until firm, about 20 minutes.

In a large bowl set over a pan of barely simmering water, stir chocolate and remaining 1/2 cup (1 stick) of butter until melted and smooth. Remove from water and whisk or beat until well blended. Stir in remaining 3/4 cup sugar, eggs, and vanilla until well blended. Stir in remaining 1/2 cup flour, baking powder and salt until well blended.

Pour chocolate mixture over caramel layer then bake in oven at 350°F until skewer comes out clean, 35-40 minutes. Let cool then cut into 24 squares.