1.) HEAT oven to 350°F. DIVIDE apples evenly among six 6-oz. greased custard cups, reserving a few pieces for garnish, if desired. PLACE cups in 13 x 9 x 2-inch baking pan.
2.) MIX sugar and flour in medium bowl. STIR IN egg yolks, milk, syrup, butter and vanilla until blended.
3.) BEAT egg whites with cream of tartar in mixer bowl with whisk attachment on high speed just until whites are stiff but not dry, and no longer slip when bowl is tilted. Gently but thoroughly FOLD yolk mixture into whites until color is uniform. POUR over apples, dividing evenly, about 2/3 cup each.
4.) PLACE pan on a rack in the center of a 350°F oven; pour very hot water into pan to within 1/2 inch of top of cups. BAKE until wooden pick inserted near center comes out clean, 30 to 35 minutes. REMOVE cups from water bath at once; COOL on wire rack at least 10 minutes.