1. Start by making the Mac and Cheese. In a large sized saucepan, melt the butter and fry the onion until soft, about 5 mins. Add the garlic and cook for a further minute, then stir through the flour. Gradually pour in the milk, whisking all the while. Add the mustard and simmer for 5-7 minutes, until you have a thick sauce. Remove from the heat and stir in the cheddar, parmesan, sun-dried tomato and taste to adjust the seasoning.
2. Cook the pasta for a minute or two less than then packet instructions then drain and return to the pan. Stir in the cheese sauce and add the basil.
3. Spread two slices of bread with a thin layer of mayonnaise, then flip over. Place a slice of Emmental or gruyere on one piece of bread and divide the mac and cheese between them, piling up and spreading out to the edges. Top with another slice of cheese and the remaining bread, mayo side up. Repeat with the second sandwich.
4. In a large frying pan, melt about half the butter until starting to froth up. Carefully place the sandwiches in the pan, frying for about 3-4 minutes on each side, adding the remaining butter halfway through. Gently press down from time to time to encourage browning and melting.
5. Serve immediately with rocket and chutney.