In a bowl, combine flour, baking powder, sugar, salt and cream of tartar. Cut in shortening until the mixture resembles coarse crumbs. Add milk, stir quickly with a fork just until mixed. Drop by rounded tablespoonfuls onto a greased baking sheet. Make a deep thumbprint in tops; fill each with 1 teaspoon of jelly. Bake at 450° for 10-12 minutes or until biscuits are browned.