Homemade raspberry jam made from frozen, unsweetened raspberries is recommended for these bars. It is better than store bought and less expensive. Make the jam at least the day before you plan to make these squares. To make raspberry jam: Place 2 cups (8 ounces) frozen unsweetened raspberries and 1/4 cup granulated white sugar in small saucepan and bring to boil over medium heat. Reduce heat and simmer, stirring occasionally, for about 20 - 25 minutes or until most of the liquid has evaporated. Do not let it burn. Remove from heat and pour into a heatproof measuring cup. You should have about 1 cup of preserves. Stir in a drop or two of lemon juice. Cover and place in the refrigerator overnight.