Cream the softened butter and confectioners' sugar together until light and fluffy, about 2-3 minutes.
Add the egg yolk and vanilla bean seeds and mix until combined.
Gradually add the sifted flour and mix just until a dough forms. Do not overmix.
Shape the dough into a disk, wrap in plastic wrap, and refrigerate for a minimum of 2 hours (or up to 2 days).
Preheat the oven to 350°F (180°C). Line baking sheets with silicone baking mats or parchment paper.
Place the granulated sugar in a shallow bowl. Scoop the chilled dough by the tablespoonful and roll into balls. Roll the balls in the granulated sugar to coat completely.
Place the coated dough balls about 2 inches apart on the prepared baking sheets.
Bake for 12-15 minutes, until the edges are lightly golden. Allow to cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.
