Cheesy Potato and Leek Gratin

Unsalted butter, 60g
Onion, 1, finely chopped
Garlic, 1 clove, finely chopped
Pure (thin) cream, 2 cups (500ml)
Leeks, 2, halved lengthways and sliced
Thyme leaves, 1 tbs, plus extra to serve
White wine, 1/4 cup (60ml)
Waxy potatoes, 750g
Parmesan, 40g, grated Cheddar, 40g, grated Mozzarella, 80g,
Nutmeg, grated, to sprinkle

Preheat the oven to 170°C fan-forced.

Set a large frypan over medium heat and melt 30g of the butter in it. Tip in the onion and garlic and let them soften for about 6 minutes, giving the pan an occasional stir.

Use a little of that buttery onion to grease the inside of the dish, then add a grind of pepper. Pour the cream into a jug and mix the leftover onion butter through it.

Back in the same pan, melt the last 30g of butter over medium-high. Add the leek and thyme, season, pop a lid on and cook for around 10 minutes — stirring here and there — until the leek collapses. Splash in the wine, take the lid off, and keep it going for another 5 minutes.

Peel the potatoes and run them through a mandoline into thin 2mm slices. Leave them dry — no rinsing or soaking, since the starch is exactly what you want.

Build the dish up about halfway, alternating layers of potato, cream, and the two grated cheeses, using half of everything as you go. Spread the leek across the top, then repeat the whole sequence with what's left: potato, cream, parmesan, cheddar. Season, and finish with a little nutmeg grated over.

Seal the top with foil and bake for an hour and a half, until a knife slides easily through the potato.

Turn the oven up to 185°C fan-forced, scatter the mozzarella across the top, and give it a final 15 minutes until golden.

Finish with a scattering of extra thyme and take it straight to the table.