Preheat the oven to 350 degrees. Add nonstick spray to an 8X8-inch casserole dish.
Add the sausage into a skillet and cook over medium heat until slightly browned. Break the sausage into pieces using a wooden spoon. Cook for 3-4 minutes.
Add the potato and onion and season with salt and pepper. Cook, stirring occasionally, for about 6-7 minutes. The onion should be softer, and the potato golden-brown.
Whisk the milk and eggs in a bowl and season with salt and pepper. Add 1/2 cup of the cheese and stir.
Put the potato and sausage mixture into the casserole dish and stir in the broccoli. Spread evenly and pour the egg mixture on top. Sprinkle the rest of the shredded cheese on top.
Put the casserole dish into the oven and ake for 30-35 minutes. Remove and let the casserole cool for a few minutes before slicing. Top with fresh chives.