Preheat the oven:
Preheat the oven to 180°C (160°C fan-forced) / 350°F. Have a 9×13-inch baking dish (or slightly smaller) ready.

Slice the potatoes:
Peel the potatoes and slice them thinly, about 3-4 mm thick. A mandoline is helpful if available.

Boil the potatoes:
Place the sliced potatoes in a large saucepan with water. Bring to a boil and cook for 2 minutes only. Drain through a colander and set aside.

Prepare the sauce:
In a medium saucepan, heat a dash of oil over medium heat. Add the chopped bacon and sauté until golden brown. Add the onions and garlic and sauté for an additional minute.

Make the creamy base:
Add the butter and let it melt. Stir in the flour and cook for 30-60 seconds to remove the raw flour taste. Gradually add the chicken stock while stirring to form a paste. Reduce the heat and slowly pour in the cream and milk, stirring to avoid lumps. Continue stirring until the mixture thickens and just starts to bubble. Remove from heat and stir in thyme, salt, and pepper.

Layer the bake:
Spread about ⅓ cup of the sauce in the base of the baking dish. Layer ⅓ of the potatoes, followed by ⅓ of the sauce, and then ⅓ of the grated cheese. Repeat the layers twice, finishing with cheese on top.

Bake:
Bake for 45-50 minutes until the dish is bubbling and the top is golden.