01 - Cream the butter and powdered sugar in a large bowl until smooth and fluffy. Beat in the vanilla extract until fully incorporated.
02 - Sift the flour and salt into the butter mixture. Mix until just combined and a cohesive dough forms, being careful not to overmix.
03 - Divide the dough in half and shape each portion into logs approximately 2 inches in diameter. Wrap tightly in plastic wrap and refrigerate for at least 30 minutes until firm.
04 - Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
05 - Slice the chilled dough into 1/2-inch thick rounds. Place cookies on the prepared baking sheets, spacing them about 1 inch apart.
06 - Bake for 12 to 14 minutes or until the edges are just beginning to turn golden brown. Remove from oven and let cool completely on the baking sheets.
07 - While cookies cool, whisk together egg yolks, granulated sugar, heavy cream, and vanilla paste in a small saucepan. Cook over medium-low heat, stirring constantly, until the mixture thickens slightly, about 4 to 5 minutes. Remove from heat and let cool completely.
08 - Spoon a small amount of the cooled custard onto the center of each cooled shortbread round. Gently spread to create an even layer.
09 - Sprinkle a thin, even layer of granulated sugar over the custard-topped cookies. Using a kitchen torch, carefully caramelize the sugar until golden brown and crispy. Let stand for 5 minutes to allow the sugar to harden before serving.