Heat a large skillet over medium/high heat. Once the pan is hot, add the chorizo or breakfast sausage to the pan and gently break the sausage up into small, meatball-like pieces. If you like smaller ground sausages, feel free to break the pieces up more.

Cook the sausage until it is partially cooked and remove it from the heat. Use a slotted spoon to remove the sausage from the pan, but leave the drippings.

Place the pan over medium heat and add the onion to the sausage drippings. Season the onion with ¼ teaspoon of salt and sautee the onions for 8-10 minutes, stirring periodically so they don’t brown or burn. Add the mushrooms and 1 tablespoon of olive oil to the pan and saute for 5 more minutes.

Lastly, add the garlic and spinach to the pan and toss. Cook until the garlic is fragrant and the spinach is wilted (~3 minutes). Remove the vegetables from the heat.

Whisk the eggs, heavy cream, and milk in a large bowl until combined. Set aside.

Spray a 9x13-inch casserole dish with non-stick cooking spray and add the ripped pieces of bread to the dish. Transfer the cooked vegetables, chorizo, 1 cup of cheddar cheese, remaining salt, pepper, and 1 cup of gruyere cheese to the bread and toss. Pour the eggs over all of the ingredients and toss everything together and press the ingredients down with a spatula or your hands.

Cover the strata and refrigerate the strata overnight.

Preheat the oven to 350ºF and remove the casserole dish from the refrigerator. Toss the strata with a spatula to loosen all of the ingredients. You don’t want the strata firmly pressed into the casserole dish to bake. Cover and bake for 30 minutes. Uncover and bake for another 30 minutes.

Add the remaining cheese to the top of the strata and bake for 10 more minutes or until the cheese is golden brown.

Remove the strata from the oven and let it rest for 10 minutes before slicing.