In a large bowl whisk together the flour, the sugar, and the salt, add the butter, and blend the mixture until it resembles coarse meal. Stir in the egg yolks, blend the mixture until it forms a dough, and chill the dough, wrapped in plastic wrap, for at least 2 hours or overnight.
Preheat the oven to 350°F. Let the dough soften slightly, roll level teaspoons of it into balls, and arrange the balls about 2 inches apart on lightly greased baking sheets. Using your thumb, make an indentation in the center of each ball, being careful not to crack the dough around the edges. (If the dough cracks, reroll it and try again.) Fill each indentation with about 1/4 teaspoon of the jam and bake the cookies in batches in the middle of the oven for 12 to 15 minutes, or until the edges are pale golden. Let the cookies cool on the sheets for 2 minutes, transfer them to racks, and let them cool completely. The cookies may be made 1 month in advance and kept frozen in airtight containers.