100g unsalted butter
600g onions, thinly sliced
100ml double cream
100g Gruyere cheese, grated
20cm ready-baked pastry case
100g Parmesan cheese, coarsely grated
salt and pepper
Melt the butter in a heavy-based frying pan over a medium heat. Add the onions and cook, stirring frequently to avoid burning, for 30 minutes, or until well-browned and caramelized. Remove the onions from the pan and set aside.
Preheat the oven to 190C/375F/ Gas 5. Beat the eggs in a large bowl, stir in the cream and season to taste with salt and pepper. Add the Gruyere cheese and mix well. Stir in the cooked onions.
Pour the egg and onion mixture into the baked pastry case and sprinkle with the Parmesan cheese. Place on a baking tray and bake in the preheated oven for 15-20 minutes until the filling has set and is beginning to brown.
Remove from the oven and leave to rest for at least 10 minutes. The tart can be served hot or left to cool to room temperature.
You can't go wrong with this, it was just so simple and really lovely. Went great with my sour cream mash and some steamed vegetables.