Toss 1 chopped plum with 1/4 cup granulated sugar, 1 teaspoon cornstarch and 1/4 teaspoon each cinnamon and salt. Microwave 3 minutes, then stir and set aside. Puree 3/4 cup cottage cheese in a blender with 1 egg, 2 tablespoons sugar and 1/2 teaspoon vanilla. Spoon onto the center of 4 prepared 9-inch crepes; fold in the sides and roll up. Cook seam-side down in a nonstick skillet with butter until golden on both sides. Dust with confectioners' sugar. Stir 1/3 cup raspberries into the plum sauce; spoon over the blintzes.