Breakfast Strata (Egg Strata)

Grease a baking dish with butter or oil.

In a frying pan over medium heat, add a spoonful of olive oil and, once hot, add the sliced red onion and the mushrooms.

Cook, stirring, until the mushrooms and onion brown and soften.

Add the spinach leaves and continue cooking for another minute.

Turn off the heat, cover with a lid and let the mixture cool.

In a large bowl, whisk together the eggs, milk, mustard, thyme, salt, pepper and nutmeg.

Once the egg mixture is smooth, add the cubed bread, the grated Gruyere and the mushroom mixture.

Stir everything together and pour the mixture into the prepared baking dish.

Sprinkle with the grated Parmesan.

Cover the dish and refrigerate for at least 30 minutes or overnight.

Bake in the preheated oven at 180°C/350°F for 45 minutes, or until set and golden at the edges.

Serve warm, topped with fresh chopped herbs.