Preheat oven to 350°F. Grease then line a 9 x 13-inch pan with parchment paper, leaving an overhang for easy removal. Set aside.
Add butter, granulated sugar, and powdered sugar to a stand mixer. Beat until smooth and creamy. Mix in vanilla and salt. Gradually add flour and mix until a soft dough forms. Do not overmix.
Press a little over half the dough evenly into the prepared pan. Cover and refrigerate the remaining dough until ready to use.
Bake for 25 minutes, or until the edges are lightly golden. Remove from oven.
While the base bakes, add unwrapped caramels and heavy cream to a medium pot. Heat over medium-low, stirring often, until smooth and melted, about 5 to 8 minutes.
Pour caramel over the baked base and spread evenly. Remove chilled dough, crumble into small pieces, and sprinkle over the top.
Return to oven and bake 25 to 30 minutes, or until lightly golden at the edges. Do not overbake.
Let cool completely at room temperature, then cut into bars. Sprinkle with flaky sea salt if desired.
Notes
Note 1: Werther’s Soft Caramels work best for these bars. Other caramels don’t melt as smoothly. You’ll need about 63 caramels total.Storage: Store leftovers tightly covered in the fridge for up to 1 week.