To prepare the potatoes

1. Add the whole potatoes (skin on) and 1/2 cup (125 ml) of tap water to a large microwave-safe container. Place the lid on slightly ajar, and cook the potatoes in the microwave for 10 minutes. You should easily be able to pierce the potatoes with a fork once cooked. If firm, continue cooking in 2-minute bursts (see note 1 for stovetop method).
2. Once the potatoes are cool enough to handle, use a butter knife to peel the skin off; it will slip off easily.
3. Slice the potatoes and layer them in a baking dish (you will need a dish approximately 25 x 15 cm/10 x 6 inches).

To make the creamy sauce

1. Preheat the oven grill (broiler).
2. Heat the unsalted butter in a small pot over low heat. Once melted, add the flour. Stir for 1 minute until a paste is formed.
3. Add the milk slowly, stirring with a whisk. Reduce the heat to the lowest setting and cook, stirring, for 6–8 minutes until the sauce thickens.
4. Once the sauce is nice and thick and coats the back of a spoon, it’s ready. Add the chicken stock powder and whisk until it’s dissolved.
5. Pour the sauce straight on top of the potatoes, taking care to distribute it evenly.
6. Top with the cheese and thyme leaves (if using).
7. Place under the grill for 2–4 minutes and cook until the cheese is bubbling and golden. Serve.