Put the plum tomatoes and red onions into a large roasting tin, cut side up. Sprinkle over the chilli flakes, garlic and thyme. Season with salt and freshly ground black pepper. Drizzle over the olive oil and place in the oven for 30-40 minutes, or until the tomatoes are very soft.
Put the roasted tomatoes into a blender or food processor and whizz until smooth. Tip the mixture back into a saucepan and add the tomato purée and stock. Bring to a simmer.
Serve with the crème fraîche and pumpkin seeds.
Freezing and defrosting guidelines
Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.
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