Beat the egg yolks with the cream in a large bowl. Stir in the bolognese sauce and tomato puree. Season to taste with salt and freshly ground black pepper.
Add the pasta and the Parmesan cheese and mix together.
In a large clean bowl, whisk the egg whites until they form peaks. Carefully fold the egg whites into the bolognese mixture.
Set the oven to 180°C/gas 4. Heat the butter in an ovenproof frying pan or skillet until foaming. Pour the mixture into the hot pan. Sprinkle over the Gruyere cheese and place into the oven for 8-12 minutes, until lightly set and golden brown.
Remove and serve immediately with a drizzle of cream or crème fraîche and some chopped chives.
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