Creamy spaghetti with avocado, tomato and smoked ham

Ingredients
375g dried spaghetti
1 onion, chopped
1 tomato, chopped
50g unsalted butter
1 clove garlic, crushed
2 tbsp plain flour
450ml milk
150ml double cream (or use extra milk for a less rich option)
150g gruyere or mature cheddar, grated
200g piece smoked ham, shredded
Small bunch chives, chopped
Salt and freshly ground black pepper
500g avocado, cut into 1cm cubes
Green salad to serve

Method
1. Preheat the oven to 180C.
2. Cook spaghetti according to packet instructions. Drain and reserve.
3. Set a heavy-based saucepan over a low heat, and sweat the onion in butter for 10-15 minutes until it starts to soften. Add the garlic and fry for a further minute before stirring in the flour.
4. Pour in the milk and cream, and bring to the boil, stirring constantly until thickened. Simmer steadily for 2-3 minutes to cook the flour.
5. Turn off the heat, and stir in half the cheese, along with the ham and chives. Season to taste with salt and freshly ground black pepper.
6. Stir through the cooked spaghetti, tomato and avocado, and spoon into a baking dish. Scatter over the rest of the cheese and bake for about 20 minutes, until golden brown and bubbling.
7. Serve immediately, accompanied by a green salad.