This is basically a sugar cookie recipe with which you can use up your leftover egg yolks from other recipes.
1 cup butter (2 sticks)
1 1⁄2 cups sugar
6 egg yolks (or 3 whole eggs)
2 1⁄2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon cream of tartar
1 teaspoon vanilla extract
1⁄2 teaspoon lemon extract
1⁄2 teaspoon orange extract
Cream butter and sugar until fluffy.
Separately, beat egg yolks and add extracts.
Add beaten egg yolk mixture to creamed butter and sugar.
In a separate bowl, whisk together dry ingredients (flour, baking soda and cream of tartar).
Add dry ingredients to creamed butter, sugar and egg mixture, mixing until well blended.
Form into balls about the size of a walnut.
Roll balls in sugar, place on greased cookie sheet or parchment lined cookie sheet, and slightly flatten.
Bake at 350 degrees F for 8 to 10 minutes, depending on desired softness/crispness.