1/2 cup (113 grams) unsalted butter, room temperature
1/4 cup (50 grams) granulated white sugar
1 large egg, separated
1/2 teaspoon pure vanilla extract
1 cup (130 grams) all purpose flour
1/8 teaspoon salt
3/4 cup (100 grams) hazelnuts, almonds, pecans or walnuts, toasted and finely chopped (SEE NOTE!)
1/2 cup jam
Preheat oven to 350 degrees F (177 degrees C) and place rack in center of oven. Line a baking sheet with parchment paper.
In the bowl of your electric mixer (or with a hand mixer), beat the butter and sugar until light and fluffy (2-3 minutes). Add the egg yolk and vanilla extract and beat until combined.
In a separate bowl, whisk together the flour and salt. Add the flour mixture to the batter and beat just until combined. If the batter is too soft to roll into balls, refrigerate for about 30 minutes.
In a small bowl, whisk the egg white until frothy. Place the chopped nuts on a plate. Roll the dough into 1 inch (2.5 cm) balls. Taking one ball of dough at a time, dip first into the egg white and then lightly roll in the nuts. Place on the prepared baking sheet spacing about 1 inch (2.5 cm) apart. Using your thumb or end of a wooden spoon, make a indentation into the center of each cookie
and fill with about 1/2 teaspoon of jam.
Bake for about 13-15 minutes, or until cookies are set and the nuts have nicely browned. Remove from oven and place on wire rack to cool.
NOTE: To toast the nuts. Spread nuts on a baking sheet and bake in a 350 degree F (180 degree C) oven for 8-10 minutes (almonds
, pecans and walnuts). The nuts are done when they are light golden-brown in color andfragrant. Toast the hazelnuts for about 15 minutes or until fragrant and the outer skins begin to flake. Remove from oven and place the hot nuts in a dish towel. Roll up the towel and let the nuts sit (steam) for a few minutes then rub the nuts in the towel briskly to remove the skins. Let cool completely. Once the nuts have cooled, place them in your food processor and process until finely chopped. Alternatively, you could chop them by hand.
Makes about 20 cookies.