Clean 1½ c. blueberries & slice 4 to 5 medium peaches, set aside. In top of double broiler combine ¾ c. sugar & 2 Tbsp. cornstarch. Gradually add 2 c. milk, stirring constantly, cover. Cook over boiling water 7 minutes, Do Not Stir. Remove cover, cook 10 minutes. In small bowl, beat 4 egg yolks. After sugar mixture has cooked for the 10 minutes, blend small amount of hot mixture into beaten egg yolks, then return to pan. Cook 2 more minutes, stirring. Remove from heat, stir in 1½ tsp. vanilla extract; Cool (will have a "custard" consistency). Whip ¾ c. heavy whipping cream, fold into cooled custard mixture, chill. Drizzle ¹/₃ c. rum or rum extract over 2 dozen ladyfingers. Place a layer of ladyfingers in deep glass dish. Cover with ¹/₃ of custard, some of the sliced peaches, & some of the blueberries. Repeat layers, ending with custard. Refrigerate until ready to serve. Top with whip cream or topping if desired, garnish.