Using a hand blender, stir the ricotta with the crème fraîche, 4 tablespoons of powdered sugar, lemon juice, vanilla flavor and salt until creamy. Spread the cream on four small bowls, cover with cling film and put in a cool place for about 2 hours.
Mix 2 tablespoons of powdered sugar with the strawberries 30 minutes before serving and let the strawberries steep. Then spread the strawberries on the cream and serve immediately.