In a mixing bowl, stir together the flour, baking soda and salt. In another bowl, combine the applesauce, peanut butter and the egg and mix until well blended. Add the flour mixture to the peanut butter mixture, stirring until smooth. Drop the batter by tablespoons onto ungreased cookie sheets. Chill the cookie sheets for 15 minutes before baking to firm up the dough. Bake the cookies at 375? for 10 minutes. Remove the cookie sheets from the oven and make a small thumbprint impression in the center of each cookie using your fingers. Bake the cookies for 5 minutes more. Allow the cookies to cool completely, then place a 1/2 teaspoon of jelly in the center of each cookie before eating. Makes about 36 cookies.