Cream 1 cup butter or margarine and 1/2 cup sifted confectioners' sugar. Add 2 cups flour, lemon extract, and 1/4 teaspoon salt; mix well.
Place about 1 inch apart on ungreased baking sheet. Bake 8 to 10 minutes or until lightly browned. Cool. Put together with filling. Roll in confectioners' sugar.
To Make Filling: Mix 1/2 cup sugar, 2 Tablespoons cornstarch, and dash of salt. Add 1/2 cup water, 2 Tablespoons butter or margarine, 2 teaspoons grated lemon rind, 3 Tablespoons lemon juice, and 3 drops of yellow food coloring. Bring to rolling boil, stirring constantly; boil and stir 1 minutes. Cool. Frost flat side of one cookie and put together with another cookie, sandwich-like. Roll in confectioners' sugar.