While these are sometimes referred to as "thumbprint" cookies, I call them "jam dots" because I use something other than a thumb to make the indentation that the jam goes into.

3/4 c softened butter
1/2 c sugar
1 egg
2 tsp vanilla
1 3/4 c flour
1/4 t salt
1 c finely chopped nuts (optional)

1. Preheat the oven to 375 degrees F (190 degrees C).
2. Mix together the flour and salt.
   
3. In a medium bowl, cream together the butter, sugar, egg, and vanilla.
   
4. Mix in flour a little bit at a time, then (optionally) add the chopped nuts.  Mix until the ingredients are distributed and a soft dough has formed.  Do not overmix.
   
5. Refrigerate the dough 15-30 minutes to firm it up.
   
6. Roll dough into 3/4 inch balls.
   
7. Place balls 2 inches apart on an air-cushion cookie sheet lined with parchment paper.
   
8. Use a round instrument to make a deep well in the center of each cookie and fill with ~1/4 teaspoon of preserves.
9. Bake for 15 to 17 minutes in the preheated oven, until the cookies just begin to brown.
   
10. Transfer from cookie sheets to rack for cooling.

Notes: 

A.  Adding chopped nuts results in a shorter and more tender crumb.  Without the nuts, the cookies are tasty and sturdy.  Making some dough with nuts and keeping some plain vanilla will add to the variety of a holiday tray.

B.  I use the rounded end of a plastic honey server to make the jam wells.  Making an even indentation helps to keep the jam from running over the edges. 

C.  I use air-cushion cookie sheets for these cookies because its difficult otherwise to bake the cookie through to the center without over browning the bottoms.

D.  Even after setting up, the jam centers can be a bit sticky.  Drizzling chocolate in thin stripes across the cookie tops will help to keep them from sticking together, as well as giving decorative flair.