Mascarpone Roulade

Preparation:

Preparation: First make the filling: finely chop the onions and cook them in a saucepan for 20 minutes with the melted butter. Add the flour and mix well. Away from the heat, slowly add the poured milk, put the saucepan back on the heat and bring to a gentle boil. When the sauce has thickened, add the chopped walnuts, nutmeg, salt and pepper. Now make the roulade (while you prepare the dough, keep the filling on a very low heat in a bain-marie): butter a sheet of greaseproof paper and line a baking sheet with high sides with it. Brush it with melted butter and turn on the oven at 200 degrees. Grate the caciotta and work it with the mascarpone: add the flour, marjoram, egg yolks, salt and cayenne pepper. Now add the whipped egg whites to stiff peaks, then pour the mixture onto the oven tray and cook for about 40 minutes. Away from the heat, spread half of the onion and walnut filling on the roulade, then gently roll it up on itself by taking one side of the wax paper, which you will remove at the same time. Cover it with the rest of the filling, sprinkling it with chopped parsley and leave it to rest in the heat. In the meantime, make the sauce: in a small saucepan, fry the chopped onion in butter, add the flour and immediately remove from the heat. Slowly pour in the milk, add the bay leaf and nutmeg and bring back to the heat. Stirring constantly, thicken the sauce, then cover it with a sheet of greaseproof paper and cook it for another half hour in a bain-marie. Adjust the salt and pepper, strain the sauce and stir in the grated horseradish, cream and lemon juice. Cut the roulade into slices and arrange them on a heated serving plate. Serve hot, with the horseradish sauce on the side.