Preheat oven to 350 degrees F.
Add egg yolks and vanilla to the bowl. Mix again until incorporated.
Add flour to the bowl. Start mixer on low speed and increase to medium speed, mixing until fully combined.
Lay a piece of parchment paper on a flat surface. Sprinkle with flour and add half of the cookie dough, placing the remaining cookie dough in the fridge.
Sprinkle the top of the dough with flour. Add parchment paper on top of the dough and use a rolling pin to roll out the dough to ¼” thickness.
Use heart-shaped cookie cutters to cut out cookies.
Use a metal spatula to carefully transfer the cookies to an ungreased baking sheet, leaving at least 1” in between cookies.
Place baking sheet in preheated oven and bake for 8-12 minutes or until edges of cookies are golden brown. Allow cookies to remain on baking sheet for 2 minutes before transferring to a cooling rack.
While cookies are cooling, prepare the chocolate frosting.