Preheat the oven to 100°C fan.

Halve the tomatoes and scrape out the seeds and excess liquid with a teaspoon. Add to a bowl. Drizzle generously with olive oil and season with salt, black pepper, chilli flakes and oregano. Toss to coat evenly.

Spread out in a single layer on a baking tray lined with parchment paper, cut side up. Place in the middle of the oven for at least 4 hours, or until the tomatoes have dried out and concentrated. They should be shrunken, slightly chewy at the edges and jammy in the centre. Not crisp.

Leave to cool completely before storing. Pack into a sterilised jar and cover with olive oil. Seal and refrigerate. Use within 2-3 weeks.