How to Make It
In the bowl of a stand mixer fitted with the paddle, beat the butter with the sugar at medium speed until light and fluffy, about 2 minutes. Beat in 1 egg yolk and the vanilla until incorporated, about 2 minutes. At low speed, beat in the flour and salt until the dough just comes together. Turn the dough out onto a work surface and pat into a disk.
On a lightly floured work surface, roll out the dough to a 1/4-inch-thick rectangle. Ease the dough into a 14-by-4-inch fluted tart pan with a removable bottom, pressing it into the corners and patching any tears. Roll the rolling pin over the tart pan to cut off any excess dough. Freeze the cookie shell for 1 hour.
Preheat the oven to 350°. In a small bowl, beat the remaining 1 egg yolk with 2 teaspoons of water. Lightly brush the shell all over with the egg wash. Bake for about 20 minutes or until pale golden. Let the cookie shell cool completely, about 1 hour.
Meanwhile, spread the pecans in a pie plate and toast for about 12 minutes until golden. Let cool.
Put the chocolate in a large heatproof bowl. In a small saucepan, bring the cream just to a simmer. Pour the hot cream over the chocolate and let stand for 5 minutes; whisk until smooth. Let the ganache cool slightly, about 20 minutes, then pour the ganache into the cookie shell. Refrigerate until firm, about 1 hour and 30 minutes. Remove the tart ring. Scatter the top of the bar with the popcorn and pecans and drizzle all over with the caramel sauce. Sprinkle with sea salt. Cut the cookie bar into slices. Serve.