Heat your oven to 180°C/Fan 160°C/Gas 4. Strip the leaves from the thyme sprigs. Peel and thinly slice the onion. Heat 1 tbsp olive oil in a frying pan. Add the onion. Season. Cook, stirring occasionally, on a very low heat for 15 mins till soft.

Add one third of the thyme leaves to the onion and ½ tbsp of the sugar. Cook for 5 mins. Remove from the heat. While the onions cook, cut the tomatoes in half. Peel and thinly slice the garlic.

Grate the cheddar. Grate the butter into a bowl. Add the flour, reserving 1 tbsp for later. Using your fingertips, rub the butter into the flour till it resembles breadcrumbs. Stir the cheddar into the buttery flour and add half of the remaining thyme leaves. Season with salt and pepper.

Separate the egg yolk (keep the white). Add the yolk to the bowl with 2 tbsp ice cold water and bring together to form a dough. Add more water, 1 tsp at a time, if necessary, but take care not to make the dough too wet.

Once you have a dough, roll it into a ball and pop into the fridge for 10 mins to rest. Once it has rested, dust your work surface with the 1 tbsp flour you saved earlier. Roll the dough into a circle slightly bigger than a small, round ovenproof pan or dish. It should be the thickness of a £1 coin.

Place the ovenproof pan on the hob. Add 1 tbsp olive oil and warm to a medium heat. Add the garlic slices and remaining thyme leaves and cook for 1 min till they sizzle. Add the remaining sugar and stir. Remove from the heat.

Place the tomatoes into the pan, cut-side down. If you have any extra, halve them again and place on top of the halves lining the pan. Spoon over the caramelised onions and spread evenly.

Place the pastry on top. Tuck the edges down into the sides. Brush with the egg white. Cook in the oven for 25 mins. Leave to cool for 5 mins. Flip out onto a plate. Serve with the peppery salad leaves.