Preheat the oven to 190°C/375F/Gas Mark 5.
In a saucepan melt the butter and stir in the flour until blended. Cook for 2 minutes over a medium heat. Gradually add the milk whisking continuously. Bring to the boil and simmer for 2–3 minutes. Add the grated Gruyère cheese and continue cooking for a further 2–3 minutes.
Remove the outer leaves and finely shred the cabbage, wash and drain well.
Place the cabbage in a large pan and add the butter, salt and pepper and just enough water to prevent the cabbage burning. Cover the pan with a lid and cook over a medium heat for 5–7 minutes until just beginning to soften. Drain thoroughly and return to the pan.
Heat a heavy-based pan over a high heat and add the bacon and dry fry until the fat runs, add the onion and continue frying until the onion is soft. Remove from the heat. Add the onion and bacon to the cabbage in the pan.
Pour over the cheese sauce and mix thoroughly. Season to taste.
Tip into a greased gratin dish, sprinkle with the remaining grated Gruyère cheese and bake in the preheated oven for 20-30 minutes until golden brown. Serve with a green salad.
*This recipe is very indulgent, so shouldn't be eaten too often. But it's great for those special occasions!
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.