Dulce de Leche Thumbprint Cookies

Preheat oven to 375 degrees. Line a baking sheet with parchment paper.

In a mixing bowl, beat together butter and sugar until fluffy.

Add the egg yolk and vanilla and beat until smooth.

Add the flour and salt and mix until well incorporated. The dough should come together to form a ball.

Scoop 1" balls of dough onto the cookie sheet, and make small indents in the top of each one with the back of a spoon.

Bake for 8 to 10 minutes or until just barely brown on top.

Remove the cookie sheet from the oven and gently re-indent the tops of each cookie.

Scoop a spoonful of dulce de leche into the indent on the top of each cookie and return the sheet to the oven to bake for an additional 3 minutes.

Cool cookies on a wire rack.