1. Crush 2 cups of macadamia nuts, or pecans.
2. Separate the two eggs.
3. Whisk the egg yolks until foamy.
4. Mix butter and sugar until fluffy.
5. Add the reserved egg yolks and blend just until mixed.
6. Add the flour, extract, and salt. 
7. Mix, scraping the bowl often, until the mixture forms a dough. Do not over-mix the dough, mix only until things come together.
8. Shape rounded teaspoonfuls (about 3 tsp.) of dough into balls. 
9. Dip each dough ball into the beaten egg whites, then roll in the chopped nuts. 
10. Place 2 inches apart on a cookie sheet lined with parchment paper. Make an indentation in the center of each cookie with your thumb or a measuring spoon back. 
11. Bake for 12-14 minutes, or until lightly browned.
12. While hot, lightly press the back of a teaspoon into each indentation to firm the shape up. Let cool.

Filling:

1. Combine and beat together the softened butter, powdered sugar, eggnog, and extract or liquor. Beat until creamy and smooth. Fill each cookie with 1/2-1 tsp. of filling. Dust with freshly grated nutmeg.
2. These cookies should be kept in the refrigerator until served.