Brush the aubergine with a little oil, season with salt and pepper, then place onto a hot griddle pan. Cook for 5 minutes on either side, or until sear marks are formed. When all of the slices are cooked set to one side.
Gently fry the onions in the remaining oil for 5 minutes. Then add the garlic, tomatoes, carrot, beans and herbs. Once it’s hot, sprinkle in the stock powder. Allow to simmer for 10 minutes. Season as required.
To make the cheese sauce: first melt the butter on a gentle heat. Then add the flour, stirring constantly. Stir for 1 minute, then add the milk a little at a time. The sauce will thicken as the heat increases. When all the milk has been added continue to stir for 2 minutes. Remove from the heat and add 100g of the cheese, stir and set to one side.
To assemble: place half the tomato sauce into a deep oven-proof dish. Top with slices of aubergine, pasta and then cheese sauce.
Repeat, ending up with a final layer of cheese sauce, making sure the pasta is covered.
Place in the oven for 30 minutes. Add the final 50g grated cheese and return to the oven for another 15 minutes.