In a large mixing bowl, cream together sugar and butter until light and fluffy, about 3–4 minutes. Beat in egg and vanilla extract, ensuring well combined. Gradually add flour, mixing until smooth.

Cover dough with plastic wrap and refrigerate for at least 30 minutes. Preheat oven to 350°F (175°C). Scoop and roll dough into balls and place on baking tray lined with parchment paper.

Bake cookies for 12–15 minutes, or until edges are lightly browned. Let cool completely on a wire rack.

In a saucepan, heat heavy cream and vanilla extract until warm. Whisk together egg yolks and sugar in a separate bowl. Slowly pour warm cream into egg mixture while whisking to prevent curdling.

Return mixture to saucepan over medium heat and stir until thickened, about 5–7 minutes. Pour into a bowl, cover with plastic wrap pressed against the surface, and cool in the refrigerator.

Once cookies and pastry cream are cool, pipe or spoon cream onto the flat side of a cookie. Top with another cookie to create a sandwich.

Sprinkle granulated sugar on top of the filled cookies and caramelize using a kitchen torch or by broiling in the oven for a few seconds.

Allow caramelized sugar to cool slightly before serving.