• Preheat the oven to 350°F. Line two baking sheets with parchment paper. Set aside.
• If the hazelnuts need to be skinned, there is an easy way to do it in my post Hazelnut Gianduja Cake. If a bit of the skins refuse to budge, it's fine. Cool completely before proceeding.
• Place the nuts in the bowl of a processor and use long pulses in the beginning, then quicker ones to chop the nuts finely. Do not process past this point or they can turn into hazelnut paste.
• Beat the egg whites, cream of tarter and vanilla on medium speed until very foamy and increased in volume. Slowly, add the sugar and beating to medium peaks.
• Fold in the hazelnuts.
• With a #60 disher/scooper or a tablespoon, drop rounds about 1 1/2" apart on the prepare sheets. 4 across and 5 down on a half sheet pan works well.
• Bake for 13 to 15 minutes until they feel crisp. The cookies are done when they can be lifted off the paper easily and cleanly.
• Cool for a few minutes and make an indentation in the middle of each cookie with the end of a wooden spoon.
• Microwave or heat the jam until it is liquid. Carefully spoon the jam into the indentations. Let the jam dry overnight or until no longer tacky.
• Store in an airtight container for a week or more. These also freeze well. Thaw at room temperature.

Alternative Fillings

• Any jam can be used as long as it is smooth and without pieces of fruit in it.

  Chocolate Filling: Use 8 ounces of semisweet chocolate and 2 tablespoons shortening or coconut oil. Microwave at half power or heat over simmering water just to melt the chocolate and shortening. Stir together and fill the indentations. Refrigerate briefly to set up. They can then be stored at room temperature.

  Nutella is another option. Hazelnut on hazelnut - can't get much better!