Direction :

1. Heat oven to 325ºF. Place spinach in a large colander and set it in the sink. Grease a 9×13-inch pan lightly with butter or with nonstick spray.
2. In a medium skillet over medium-high heat, heat the oil till it shimmers. Cook the sausage till it browns and is nearly cooked through, about 5 minutes. Break it up with a spoon or a spatula as it cooks. Spoon the sausage over the spinach in the colander in the sink. Return the skillet to the stovetop, add a little bit more oil to the pan if necessary, and set it over medium heat. Add the onions. Season with salt. Cook the onions till they begin to caramelize, 7 to 10 minutes. Spoon the onions over the sausage and toss with a spatula or large spoon to gently wilt the spinach. Transfer the spinach-sausage mixture to the prepared pan. Spread the cheese over top.
3. Break the eggs into a large bowl, season with 1 to 1.5 teaspoons salt (when I am using Morton’s kosher salt, I use 1 teaspoon; when I use Diamond Crystal, I use 1.5 teaspoons) and fresh cracked pepper to taste. Add the half and half, and beat with a whisk until the mixture is well blended. Pour the eggs into the pan. Season with more pepper to taste. (Note: You can strategically pull leaves of the spinach from the custard so they are at the very top, where they will stay during the baking process — this is purely for visual effect.) Transfer pan to the oven and bake for 25-40 minutes, rotating the pan halfway through. Start checking at 25 minutes, then every 5 minutes thereafter till it’s done — depending on your oven and the material of the pan you are using, it may take more or less time to cook.