In a medium saucepan, combine sugar, cornstarch and tomato pieces. Cook over low heat, stirring constantly, until very thick. Add grated rind and juice of 1 lemon, stir well and heat again to bubbling. Chill thoroughly.
For the cookie batter, cream granulated sugar and butter till fluffy. Add egg and milk and blend well. In a small bowl, combine flour, soda, cream of tartar and salt. Add to creamed mixture and blend well Chill at least 1 hour.
To assemble cookies, roll chilled dough to 1/8" thickness and cut cookies with the outer ring of a doughnut cutter, or cookie cutter. Top half the cookies with 1 tbls of chilled filling. Using the center ring from the remaining half of the cut out cookies and place on top of filled halves. Crimp edges with a fork to seal and bake in a 350* oven 15-20 minutes, or until lightly browned.