2/3 cup butter, softened
1/2 cup sugar
1 teaspoon vanilla
1 1/2 cups all purpose flour
1/3 to 1/2 cup jam or preserves
Separate egg whites and yolks in separate bowls. Chill the egg whites until needed.
In a stand mixer or an electric mixer, cream butter for about 1/2 min. Add sugar and continue creaming until the butter is light and fluffy. Add in egg yolks and vanilla. Add the flour and stir on low to medium speed until all the flour has been combined. Chill the dough for about 15 mins or until it is slightly firm.
Shape the dough into little balls of dough about 12 g each (about 1 teaspoon). Press the dough ball into the cookie mold and then depress the plunger to release the dough. Lay the shaped dough out on a cookie sheet lined with parchment paper.
Continue shaping cookies until all the dough has been used up. Freeze the shaped cookie dough for 1 hour as it will help the shaped cookie to hold its shape better during the baking process.
In the meantime, preheat oven to 375 F. Put the chilled trays of cookie dough directly in the middle rack of the oven and bake for 10 mins.
Remove from oven and fill the center with the selected jam or filling of your choice. Brush dough with egg whites.
Return the cookies to the oven for another 5 mins for a final bake.