A fool is a simple dessert made with fresh fruit and whipped cream.
In a small, nonreactive saucepan, combine blueberries, lemon juice, granulated sugar, and 2 tablespoons water. Cook over medium heat, stirring frequently, until blueberries begin to break down and juices boil and thicken, about 5 minutes. Remove from heat, and transfer to a small bowl. Place bowl in a larger bowl of ice water, and stir mixture occasionally until cold.
In a separate bowl, combine cream, confectioners' sugar, and vanilla. Beat until stiff peaks form; fold in 1/3 cup of the blueberry sauce. Divide among 4 dessert dishes, and spoon remaining sauce over tops.