Prepare the barbecue for indirect cooking over medium heat (190°C to 230°C- roasting setting). If using a Weber Q barbecue, set up your barbecue with a convection tray and a trivet.
Spray a Weber Ware Frying Pan lightly with oil. Arrange a layer of potatoes over the base of the pan, slightly overlapping. Top with one-third of the bacon and onion. Repeat this process twice so you have three layers in your pan.
In a bowl combine the cream, milk, and mustard and mix together. Pour over the potato mixture. Cover the pan with foil.
Bake the potato bake over indirect medium heat, with the lid closed, for 30 minutes, then remove the foil and bake for a further 30 minutes.
Bake the potato bake over medium heat, with the lid closed, for 30 minutes, then remove the foil and bake for a further 30 minutes.
Top with the cheese and continue baking until the potatoes are tender, another 30 minutes. Remove from the grill and season with salt and pepper.