In the top of a double boiler combine eggs, sugar, lime peel, and lime juice. Stir to mix well. Add butter. Stir over very gently simmering water until lime curd is thick enough to mound slightly. Remove double boiler top from heat; let lime curd cool, then cover and chill until cold or up to 3 days. Stir and spoon equally into tart shells. Serve cool or at room temperature, garnished with mint sprigs. Makes 24 tarts. Per tart: 190 cal. (57 percent from fat); 2.2 g protein; 12 g fat (7.4 g sat.); 18 g carbo.; 129 mg sodium; 66 mg chol. BAKED TART SHELLS In a bowl or food processor combine 1/4 cup powdered sugar, 2 cups all-purpose flour, and 1 cup (1/2 lb.) butter or margarine. Rub with your fingers or whirl until very tine crumbs form. Pat into a ball or whirl until dough forms a ball. Divide in 24 equal pieces. Press each piece evenly into a 1-1/2-inch-wide tart pan or muffin cups, making dough flush with pan rim. Set on a baking sheet and bake in a 400° oven until golden brown, about 12 minutes. Let cool on racks, then remove from pans. If making ahead, package airtight and freeze. dess106