Strata with caramelized onions and breakfast sausage

Ingredients:

• 1 tablespoon unsalted butter, room temperature
• 1 tbsp. l. olive oil
• 350 g uncooked breakfast sausages, casings removed
• 1 large onion, thinly sliced
• 3 cups low-fat cream (10%)
• 1/4 tbsp. grated parmesan
• 10 large eggs
• 1 loaf (350g) sourdough bread (crusts removed), diced, preferably stale (about 6 cups)
• 2 tbsp. grated muenster

Preparation:

1. Grease a 22x32cm baking dish with butter.
2. Heat the olive oil in a large skillet over medium heat. Add the sausage and cook, breaking up any large lumps with a wooden spoon, until browned, about 5 minutes; transfer to a bowl with a slotted spoon. Add the onion to the skillet and cook over medium heat, stirring occasionally, until very soft and golden, 20-25 minutes. Increase the heat to medium-high and cook, stirring frequently, until golden brown, another 6 minutes. Set aside.
3. In a large bowl, combine the cream, Parmesan, eggs, 1 1/2 tablespoons salt and some freshly ground black pepper.
4. Place half the bread cubes in the prepared baking dish. Sprinkle with 1.5 cups of Muenster, then add the sausage-onion mixture. Top with the remaining bread cubes and pour the cream mixture evenly over the top. Cover with plastic wrap and refrigerate overnight. You can let the mixture rest for 30 minutes to 1 hour before baking.
5. On the day of baking, preheat the oven to 160°C.
6. Let the casserole stand at room temperature while the oven preheats. Remove the plastic wrap and sprinkle with the remaining 1/2 cup Muenster. Bake until the bread is slightly puffed and the liquid has set in the center, 40-50 minutes. Let it rest for 5 minutes and serve.