1. Preheat the oven to 180°C/350°F/gas mark 6. Heat a little olive oil and the butter in a frying pan, add the onion, thyme and nutmeg and cook gently for 5 minutes until the onions are softened but not browned. Tip the cooked onions into a large Pyrex bowl and add the breadcrumbs. Pour over the milk and leave to stand for 5 minutes to allow the breadcrumbs to soak up the milk.
2. Mix in the remaining ingredients, season with salt and pepper then press into the bottom of the square Pyrex dish. Bake in the oven for 35-40 minutes until golden brown on top.