Heat the oven to 200C/180C fan/gas 6. Fry the mushrooms in a large non-stick frying pan over a medium-high heat until the liquid has released and evaporated, about 8-10 mins. Add 1/2 tbsp oil and fry until golden, about 2 mins. Remove from the pan and tip into a large bowl.

Wipe out the pan to remove any excess liquid, then return to a medium heat. Add the remaining oil and fry the sausages until golden all over. Remove using a slotted spoon and add to the bowl with the mushrooms. Fry the onions and peppers, stirring occasionally for 8-10 mins until soft but not browned. Tip into the bowl with the sausages and mushrooms, and mix everything together to combine. Season well. Tip the sausage and veg mixture into a baking dish (around 35 x 25cm) or roasting tin. If you’re using a tin, you may need to oil it to prevent the casserole from sticking.

Combine the eggs, milk, cheddar and chives in a large jug, season well, then pour this over the ingredients in the dish or tin. Bake for 25-30 mins until golden and set. Leave to cool slightly before cutting into squares.