Preheat oven to 165°C bake. Grease a large baking dish.
Melt 20g butter in a large frying pan on medium-high. Sauté spinach to remove some of the moisture. Remove from pan and leave to cool a little, then squeeze out any excess water.
In the same pan, melt remaining 30g butter on medium heat. Sauté broccoli, mushrooms, onion and garlic until tender (about 5 minutes). Add spinach back to pan and cook for a further 2 minutes. Set aside.
Tear the bread into pieces. Layer half the bread, cheese and veggie mix into prepared dish, then repeat to form another layer.
In a large bowl or jug, whisk together eggs, cream, milk, mustard, salt, pepper and nutmeg until well combined. Pour into the baking dish, cover and leave to soak for approximately 1 hour.
Bake for 45-55 minutes, until golden brown and just set.