Preheat oven to 190 degrees. Line two baking sheets with parchment paper or silicone mats. In a large bowl, use a mixer to beat the butter, peanut butter and sugar together on medium speed, 3 to 4 minutes. Add vanilla extract and egg yolk and whisk. Reduce mixer speed and add flour, beat.
Whisk 2 egg whites in a bowl with a fork. Place the chopped peanuts in another bowl. Form small balls from the resulting dough. Dip them in the protein mixture until the balls are completely covered in the mixture. Then roll the balls into the chopped peanuts, if you are using it. Place the balls on prepared baking trays at a distance of 5 cm from each other. Press down lightly on each ball with your finger or the end of a wooden spoon to make a depression in the center.
Bake cookies for 15-18 minutes until light golden brown. Put the finished cookies on the counter and cool to room temperature. Repeat with the rest of the test.
Place the preserves or marmalades in a small saucepan and bring to a boil over low heat, stirring occasionally. Using a small spoon, fill the holes in the cookies with hot jam. Let the jam cool to room temperature. Store cookies in an airtight container at room temperature for 4 days or up to 2 months in the refrigerator.
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