Preheat the oven to the highest possible top heat or grill. Sort the raspberries, wash briefly and pat dry. For the gratinating mixture, mix the egg yolks with the powdered sugar, sparkling wine, lemon juice and zest and whisk over a hot water bath until foamy. Remove the bowl from the water bath and carefully fold in the curd cheese and cream. Divide three quarters of the berries among small, shallow gratin dishes or ovenproof plates and pour the gratin mixture over them. Sprinkle the remaining berries on top and press them in a little. Bake in the oven (preferably under the broiler) on the middle rack until the top is golden. Remove the gratin, sprinkle with powdered sugar and serve in the dish.