Easy sausage casserole

Caroline's tips for the perfect sausage casserole:

If you want to make this ahead, the casserole keeps well in the fridge for up to two days. Simply reheat gently on the hob or in the oven until piping hot, adding a splash of water if it looks a little thick.
For extra flavour, I sometimes brown the sausages before adding them to the casserole. It takes a few extra minutes, but is well worth it for the caramelised taste.
To make the casserole go a little further, I sometimes add diced carrots or mushrooms along with the onions, celery and peppers. Alternatively, you could add a handful of chopped spinach or kale towards the end of cooking for an extra boost of greens – it wilts down nicely and adds a lovely colour to the casserole and is a good way of using up the end of a bag or bunch of veg that might go to waste.
You can also add an extra boost of beans by using more than one variety; this will add fibre.