Beat the butter with the sugar on medium speed for 3 minutes.
½ cup unsalted butter,, ½ cup sugar
Add the egg yolk and vanilla extract, beat for 2 more minutes. Keep the egg whites for later in a bowl.
1 large egg, 1 tsp vanilla extract
Add sifted flour and salt, mix at the slowest speed just until combined.
1 cup flour,, ¼ tsp salt
Mix the almond flour with 2 tbsp of sugar in a small bowl. Place the egg whites in a separate bowl.
1 large egg, ½ cup almond flour,, 2 Tbsp sugar,
Make 11 balls out of the dough. Dip each ball into the egg whites, then into the almond flour. Lay out on a baking sheet lined with parchment paper. Make a dent in the middle of every cookie with your finger.
Bake for 10 min, then take out from the oven. If needed press lightly again to make the deeper indentations.
Fill each dent with jam, then cook for 8-10 more minutes, until golden brown.