Step 1

Preheat the oven to 170c (fan) or 180c (regular)

Step 2

Butter a gratin dish

Step 3

Peel the onion, potatoes and garlic

Step 4

Use a mandolin set to 3/8cm to cut the onion and potato into neat slices

Step 5

Chop the garlic into tiny nuggets

Step 6

Strip the thyme of any large stalks

Step 7

If your onion is strong, melt a little butter in a frying pan and gently fry the onion slices for 5 - 8 minutes till soft

Step 8

Start building the dish with a layer of onions

Step 9

Season with salt and pepper, add a few thyme leaves and a few bits of garlic

Step 10

Add a layer of potatoes

Step 11

Repeat until the dish is full, finishing with a neat layer of potatoes.

Step 12

Press the mixture down gently but firmly

Step 13

Pour over the stock

Step 14

Finish the dish by dotting with little bits of butter, seasoning with salt and pepper and sprinkling over any remaining thyme

Step 15

Cook in the oven for an hour in total.

Step 16

After 30 minutes, check and add more stock if necessary. If the potatoes are browning then cover the dish with foil.

Step 17

Remove the foil for the last 10 minutes of cooking