Step 1 Par boil the potato slices in boiling, salted water for about 5 minutes, then drain in a colander and refresh with cold water.
Step 2 Sauté the bacon in a splash of olive oil until crisp and golden. Add the onions and cook for about 10 mins until the onions are soft.
Step 3 Butter a gratin dish and arrange layers of potato, onion and bacon and cheese, seasoning as you go but don’t add too much salt.
Step 4 Pour the cream over and bake for 40 mins at 190′C/ fan 170′C/ top of baking oven in Aga until the top is golden and bubbling.
Step 5 Serve with some cherry tomatoes, olive oil, sea salt and basil for a wonderful lunch or supper dish.