Cream the butter with the sugar then add the egg, beating well. Sift the flour and salt together, then add all at once to the creamed mixture, beating with a spoon, finally mixing with the hands until dough is soft and pliable. Refrigerate for at least 2 hours before rolling. Since this is an extremely short dough, roll on floured pastry board or between 2 sheet of waxed paper to a 1/4'' thickness. Cut in 3-inch rounds.
Cut the centers out of half the rounds. Use a small cookie cutter or a pillbox. Bake rings and rounds in a 375F oven for 7 to 10 minutes.. or until edges are slightly browned. Cool on rack, place a dab of raspberry preserves, strawberry jam or apricot jam on each round, then place a ring, sandwich style, on top or this. Dust the tarts- with confectioner's sugar. Makes about 2 dozen.