For the crust:
1-1/2 cups all-purpose flour
3/4 cup confectioners sugar
1/4 teaspoon fine sea salt
6 ounces (12 tablespoons) chilled unsalted butter, cubed
1/2 teaspoon vanilla bean paste or pure vanilla extract

For the filling:
1 pound good-quality semisweet chocolate, chopped
3/4 cup whole or 2% milk
4 ounces (8 tablespoons) unsalted butter, cubed
4 large eggs
2/3 cup granulated sugar
3 tablespoons Kahlúa (or 2 teaspoons vanilla)