Step 1

Preheat oven to 350°F / 175°C. Line a baking sheet with parchment paper and set aside.

Step 2

With a handheld or stand mixer fitted with a whisk or paddle attachment, beat butter and sugar on medium speed until creamy for about 1-2 minutes.

Step 3

Add egg yolks, salt, and vanilla* and mix for about 1 minute.

Step 4

Stir in flour until it comes together on low speed. Knead by hand a few times until smooth.

Step 5

Separate the dough into 40 equally sized portions. Form balls with your hands and roll in sugar, sprinkles, nuts, or whatever you like.

Step 6

Place half of the cookies on the prepared baking sheet with about 1.5-2 inches space in between. Press the back of a 1/2 tsp in the center and fill up with chocolate, nuts, jam, peanut butter, or Hershey kisses.

Step 7

Bake one sheet after another for about 9-10 minutes until they look pale, puffed, and matte. Let cool on the baking sheet for about 5 minutes then transfer to a wire rack and let cool completely. They will stay fresh in an airtight container at room temperature up to 2 weeks or freeze up to 1 month. When freezing, let them thaw overnight in the fridge and let them come to room temperature before serving.