Preheat the oven to 325°F. Butter a 9x13 baking dish or line it with parchment paper.
Beat butter, sugar, and powdered sugar together on medium speed until creamy. Add the vanilla and beat until combined.
Add the sifted flour on low speed and mix until a smooth, soft dough forms.
Press one-third of the dough into an even layer in the prepared pan. Bake for 20 minutes, until the edges are pale golden brown. Refrigerate the remaining dough while the crust bakes.
While the crust bakes, place the unwrapped caramel candies and cream in a microwave-safe bowl. Microwave on high for 1 minute, then stir until smooth. If any candies remain unmelted, continue in 30-second intervals, stirring after each, until fully smooth. Stir in the vanilla.
Pour the caramel filling over the baked crust, sprinkle evenly with the coarse sea salt, and crumble the remaining chilled dough over the top.
Return the pan to the oven and bake for 25 to 30 minutes, until the filling is bubbling and the topping is firm and lightly golden. Cool completely before cutting into squares.
Notes
Yield: 24 bars from a 9x13 pan, or 16 bars from an 8x8 pan using a halved recipe. Doneness Cue: The filling should be visibly bubbling at the edges and the crumble topping should feel firm, not soft, when the pan is gently shaken. Storage: Wrap bars tightly in plastic wrap and refrigerate for up to one week. Bring to room temperature for about 15 minutes before serving if you prefer a softer texture. Make Ahead: Bake and cool completely, then wrap the pan tightly and refrigerate up to one day ahead for cleaner slicing.