In a large sauté pan on a medium heat, gently sweeten the onion, leek, thyme and salt in the butter for 8 minutes – cover the pan with a lid to prevent them from colouring.
Remove the lid, increase the heat to high and add the sliced bacon.
Continue to cook for 2 minutes until the bacon begins to crisp slightly.
Remove the pan from the heat, add the sliced potatoes, half the Saint Agur blue cheese and gently mix.
Preheat the grill to high.
Spoon the potato mixture evenly into the oven-proof dish, top with the remaining Saint Agur blue cheese. Add the enough cream to come halfway up the vegetables in the dish.
Place under the hot grill, reduce the heat to medium and gratinate for 5 minutes, or until golden and bubbling.
Leave to rest for a few minutes before topping with the chopped chives. Serve immediately.