Bring the cassis, 250 ml water, 50 g sugar and 4 tablespoons lemon juice to the boil. Peel and add the pears and simmer for about 45 minutes in a closed pot. (If the pears are not covered turn them over in between.) Chop the walnuts. Caramelise 3 tablespoons of sugar, roast nuts briefly in it. Put the brittle immediately on a baking tray or tray lined with baking paper and spread a thin layer.
For the crème, whip vanilla sugar, cream, crème fraîche, 5 tablespoons of sugar, 1 tablespoon of lemon juice and cream firming agent with the whisks of the hand mixer. Remove the finished pears from the stock. Reduce the stock to a syrupy consistency. Arrange cream, pears, brittle and syrup on plates