1. Preheat the oven to 200°C (400°F).
2. Heat oil in a large skillet over medium-high heat and brown onions for 10 minutes.
3. Add mushrooms and sauté for about 5 minutes. Season.
4. Add the spinach at the last moment and cook until slightly wilted. Set aside.
5. Butter the slices of bread and place them in a 23-cm (9-in.) square baking dish. Divide slices evenly to cover bottom of pan.
6. Top bread with onion, spinach, and ricotta mixture.
7. In a bowl, whisk together the eggs and ricotta; pour over the vegetable mixture.
8. Top with a layer of grated cheddar.
9. Bake in oven for 20 minutes or until toothpick inserted into centre comes out clean.
10. Place under the broiler for 5 minutes.

This recipe is courtesy of Tablée des chefs.