Baked eggs with mushrooms and spinach

Ingredients:

• 230 g of sliced ​​porcini mushrooms
• Coarse salt and freshly ground black pepper
• 6 cups (about 170 g) baby spinach
• 6 slices potato bread, lightly toasted
• 2 tablespoons extra-virgin olive oil, plus more for greasing
• 1 small onion, chopped
• 6 eggs of category CO
• 1/2 cup milk
• 3/4 tbsp. grated gruyere cheese

Preparation:

1. Heat olive oil in a large skillet over medium-high heat. Add the onion and cook, stirring occasionally, until golden brown, about 8 minutes.
   
   Add the mushrooms and cook, without stirring, until they begin to brown, about 2 minutes. Add 1/2 teaspoon salt and pepper to taste. Continue cooking, stirring occasionally, until softened, about 4 more minutes. Add the spinach and cook until wilted, about 2 minutes. Remove from heat and let cool.
2. Grease a 9 x 13-inch baking dish with olive oil. Place the bread in a single layer, slightly overlapping the edges, then top with the mushroom and spinach mixture. If making ahead, cover and refrigerate overnight.
3. Before baking, preheat the oven to 180°C. Crack one egg onto each slice of bread, season with salt and pepper. Pour milk evenly over the surface and sprinkle with cheese. Bake until the egg whites are set, 25-30 minutes.