Preheat the oven to 220°C (fan), 200°C, or Gas Mark 7.
Melt the butter in a saucepan, stir in the flour, and return to the heat to cook for 30 seconds. Gradually add the milk and simmer until thickened. Next, add the crumbled goat's cheese, salt, pepper, and the tomatoes.
The next step is to add the egg yolks.
Whisk the egg whites—adding one tablespoonful first to loosen the mixture before folding in the rest—and fill the small pots with the mixture.
Place them in a roasting tin and surround with boiling water.
Cook for about 18 minutes until golden. Place in a greased roasting dish and sprinkle with half the cheese. Add the Worcestershire sauce to the passata and pour into the dish. Turn the soufflés out into the sauce and sprinkle with the remaining cheese. Then return to the oven for about 10–15 minutes to brown the cheese.
Cut the leeks into long, thin strips and fry in Welsh butter. Serve the soufflé in a pool of passata, topped with the leeks.