Preheat oven to 180°C (160°C fan-forced). Peel and slice potatoes into approx. 5mm thick slices. Layer ⅓ on base of a 5cm deep, 20cm x 25cm baking dish, slightly overlapping. Scatter over some of the sliced onion and repeat layering until all the potatoes and onion are used, finishing with a layer of potatoes.
Combine Bulla Cooking Cream, Bulla Crème Fraîche, garlic and thyme in a saucepan. Heat until mix just comes to the boil and pour over the potatoes.
Sprinkle cheese and bacon over the top of potatoes and season. Cover with foil and bake for 45 minutes. Remove foil and continue cooking for a further 20 minutes until golden and cooked through.
Sprinkle with spring onion just prior to serving if desired.