1 Preheat the oven to 220°C/200˚C fan/gas mark 7. Place a large frying pan on a high heat and add the olive oil. When the oil is hot, tip in the bacon pieces and cook for 5-10 minutes or until browned and slightly crisp.
2 While the bacon is cooking, lay out the bread slices in a 20x30cm ovenproof dish. When the bacon is cooked, remove from the pan with a slotted spoon and scatter over the bread.
3 Place the Parmesan, Mozzarella and Gruyère in a food processor with the eggs and whiz for about one minute or until smooth. Season with salt and pepper to taste.
4 Pour the egg and cheese mixture over the bread and bacon, then sprinkle over the grated Cheddar and chopped chives and season with pepper. Place the dish in the oven and bake for 15-20 minutes or until just set in the middle and puffed up and golden brown on top.