• Roast the potatoes

  Preheat oven to 425°F.

  Toss diced potatoes with 1 teaspoon oil, salt, and pepper.

  Roast 15–20 minutes, just until tender, not browned.

  Set aside to cool.

  Cook the sausage

  Brown sausage in a skillet until fully cooked.

  Remove sausage from the pan and set aside.

  Leave the fat in the pan, add 1 tablespoon butter only if needed.

  Cook the vegetables

  Add onion and red bell pepper to the pan.

  Cook about 5 minutes, just until softened.

  Add spinach and cook 1–2 minutes, just until wilted.

  Remove from heat.

  Cool before assembling

  Allow the potatoes, sausage, and vegetables to cool slightly.

  Make the custard

  In a large bowl, combine eggs, Greek yogurt, milk, Italian seasoning, kosher salt, white pepper, and nutmeg.

  Mix until smooth, by hand or with a hand mixer.

  Assemble

  Butter a 9×13-inch baking dish.

  Spread cooled potatoes evenly on the bottom.

  Sprinkle sausage over the potatoes.

  Add the vegetable mixture, then top with shredded cheese.

  Pour custard evenly over the casserole.

  Chill overnight

  Cover tightly and refrigerate 8–12 hours.

  Rest before baking

  Remove casserole from the refrigerator and let sit at room temperature for 15–20 minutes.

  Bake

  Bake uncovered at 350°F for 45–60 minutes, until the center is set.

  Rest and serve

  Let rest 10–15 minutes before slicing.

Note

• This casserole can be baked immediately after assembly. The overnight rest improves texture, but is not required.