Wash and drain blueberries. Squeeze the lemon. Mix the mascarpone, honey and rum / cognac with a whisk, add lemon juice and stir in. Caramelize sugar in a saucepan, deglaze with grape juice and bring to the boil while stirring until the caramel comes off the bottom. Add the blueberries to the caramel sauce and heat briefly. Put the lemon mascarpone in bowls and pour the sauce over them.