1. Heat oven to 180°C/160°C fan/Gas Mark 4. Grease an ovenproof dish with the butter.
2. Cut the bread into large cubes and arrange in the greased dish. Tuck the sliced mushrooms between the bread. Sprinkle over the chopped rosemary and garlic.
3. Whisk the milk, eggs and egg yolks together, and season with salt and pepper. Pour over the bread and gently push the bread down in the liquid.
4. Leave to stand for 5 mins. Scatter the cheese over the top, then bake for 35-40 mins until golden and just set.
5. Serve with a crisp salad.