I have always adored jam filled anything! Jellyroll, Trifle, Thumbprint Cookies,..you name it! These are the easiest cookies in the world to make and they are by far some of the best you will ever have. If you have priced cookies made with real butter in the store recently, you will know that it makes good economical sense to make them yourself. You may have to keep your eye out for commercially made Lemon Marmalade or Jam. I believe I purchased my jar imported from Italy at World Market. Do not mistake Lemon Curd for Jam. Lemon Curd is perishable at room temp and should not be used here.
In a large mixing bowl combine all ingredients except the marmalade/jam. Mix with hands until quite smooth and well mixed.
Make 1 1/4 inch balls of dough by hand and place on an ungreased cookie sheet. Make an indentation in the center of each ball with your thumb. Fill the indentation/well with about 1/3 tsp or so of marmalade or jam. Do this with a small spoon. Do not overfill.
Bake in a 350 degree oven for 14 - 15 minutes. For convection ovens, use 325 degrees for the same amount of time.
Remove from cookie sheet with a spatula to cool completely on a rack. Do not stack.
Store airtight between layers of waxed paper. Makes 28 absolutely luscious cookies.