I just love Thumbprint Cookies because of their versatility. The jams may be any flavor you choose. You can also use lemon curd or chocolate icing if you prefer. You can make these with or without the nuts and just roll them in sugar. I even made some rolled in green-colored sugar and filled them with strawberry jam for the Christmas holidays.
Beat butter until creamy. Gradually add sugar. Add egg yolks (reserving egg whites for later) and extract. Mix out 1 cup of flour and add salt to it. Gradually add to butter mixture. Add other cup of flour gradually. Cover and chill at least 1 hour or overnight. Also make sure reserved egg whites are covered and refrigerated, too.
Preheat oven to 350 degrees F. Very lightly grease 2 cookie sheets. Set counter for the rolling process by setting out low-sided bowl with lightly beaten and reserved egg whites and another low-sided bowl for the nuts. Roll dough into 1 to 1-1/2 inch balls. Then roll each ball into egg white and then nuts. Place on cookie sheets 2 inches apart. Press thumb into each cookie before baking. Bake for 15 minutes. Cool 1 minute on cookie sheet. Move to wire racks for cooling. Press centers again with thumb. When cookies are almost cool, fill centers with jam.
* You may also coordinate the extract with your choice of nuts. Blanched almonds with almond extract, walnuts with black walnut extract, pecans with butter pecan and so on.
**Sugar maybe substituted for the nuts. I rolled some cookies in color sugar, in raw sugar and in regular granulated sugar. The sugar seemed to work better without rolling them in the egg whites, but they better kept their shape with the nuts.
*** When I used a denser preserve, I put some in a glass bowl and heated (5 or 10 seconds only) it in the microwave to thin it out a little. Also, you can make it really easy on yourself by purchasing jams and/or jellies in squirt bottles. If you cool the cookies completely, the holes can be filled with flavored icing instead.
Makes about 3-1/2 dozen.
