Strata with caramelized onions, spinach, and Gruyere with roasted cherry tomatoes

Ingredients:

• 6 cups day-old French bread, diced
• 2 tbsp unsalted butter, plus extra for greasing the pan
• 1 tbsp. l. rapeseed oil
• 2 large Spanish onions, halved and thinly sliced
• 1 teaspoon of sugar
• 1 package (280g) frozen chopped spinach, thawed and squeezed out
• 10 large eggs
• 3 cups whole milk
• 1 cup heavy cream
• 2 cups grated aged Gruyere (about 200 g)
• 2 teaspoons Dijon mustard
• 1 tbsp finely chopped fresh thyme
• 1/8 tsp freshly grated nutmeg
• 3 tbsp. l. rapeseed oil
• 4 cups cherry tomatoes
• 3 tablespoons chopped fresh chives

Preparation:

1. Preheat oven to 160°C (325°F). Place the bread on a baking sheet and toast until lightly golden brown on both sides, about 10 minutes. Remove and let cool.
2. Meanwhile, heat the butter and canola oil in a large skillet over medium heat. Add the onion and stir to coat, then add the sugar, salt, and pepper. Cook, stirring occasionally, until the onion is golden brown and caramelized, about 20 minutes. Remove from heat and let cool slightly.
3. In a large bowl, combine the toasted bread, caramelized onions, and spinach. In another large bowl, combine the eggs, milk, heavy cream, 1 1/2 cups cheese, mustard, 1 teaspoon salt, 1/2 teaspoon black pepper, thyme, and nutmeg. Grease a 9x13-inch baking dish. Spoon the bread mixture into the dish, then pour the egg mixture over the bread and press down to completely submerge.
4. Increase the oven temperature to 350°F (175°C). Bake the strata, uncovered, until golden brown on top, 50 minutes to 1 hour; sprinkle with the remaining 1/2 cup of cheese 10 minutes before finishing. Let cool for 5 minutes before serving.
5. Meanwhile, prepare the tomatoes.:
   
   Heat canola oil in a large skillet over high heat. Add cherry tomatoes, season with salt and pepper, and cook until softened, 4–5 minutes. Stir in chives and remove from heat. Serve the strata with the fried tomatoes.