Heat 1tbsp of the oil in a large nonstick frying pan and add the onion. Fry over a medium heat 5 minutes or until soft and starting to colour, stirring regularly. Add the garlic and cook for a further minute. Increase the heat and add the courgettes and peppers. Cook for 3 minutes, stirring constantly.
Slowly and carefully pour the vegetable stock into the pan and add the tomatoes, tomato purée, oregano, thyme, bay leaf and sugar. Bring to a simmer and season with the salt and plenty of ground black pepper. Simmer uncovered for 15 minutes or until the vegetables are starting to soften and the sauce has thickened, stirring occasionally. As soon as it is cooked, turn off the heat and leave to stand.
While the vegetables are simmering, prepare the sauce for the topping. Pour the soya milk into a large sauce pan and add the onion, bay and thyme. Bring to a fast simmer, then immediately remove from the heat and leave to infuse for 30 minutes.
While the sauce is infusing, prepare the aubergines. Preheat the grill to its hottest setting. Cut the aubergines into diagonal slices around 1cm thick. Place as many slices as possible in a single layer on a large baking tray. Brush with a little of the sunflower oil. Cook the aubergine under the hot grill for 5 minutes or until lightly browned.
Turn the slices over with tongs and brush with some of the remaining oil. Grill for a further 5 minutes then remove from the tray and drain on kitchen paper. Cover the baking tray with another batch of aubergine slices and grill in the same way. Continue until all the aubergine is cooked and drained.
Preheat the oven to gas 6, 200°C, fan 180°C. To make the topping, strain the infused milk into a jug, discarding the onion and herbs. Stir the nutmeg into the flour. Melt the sunflower spread in a large nonstick saucepan over a low heat and stir in the flour. Cook for 1 minute, stirring constantly.
Pour a little of the soya milk into the pan, stirring continuously. When the milk has been absorbed add a little more. Continue gradually adding the soya milk until it has all been used. Bring the sauce to a simmer and cook for 2 minutes, stirring. Remove from the heat and season with salt and pepper.
To assemble the moussaka, gently pour the tomato and vegetable sauce into a 2 litre ovenproof dish – a lasagne dish is ideal. Place the aubergine slices on the top, overlapping where necessary. Pour over the white sauce so that it covers all the aubergine. Bake in the oven for 30-35 minutes until bubbling and golden brown in places.
*Some vegan products may only be available in limited stores.
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