Prep the Potatoes – Wash, peel (optional), and thinly slice. Par-cook by steaming, boiling, or microwaving for 3–4 minutes until slightly tender.
Make the Egg Mixture – In a bowl, whisk eggs, milk, salt, pepper, cheese (reserve some for topping), and most of the chives.
Assemble – Grease the baking dish. Layer half the potatoes, pour half the egg mixture, repeat, and top with remaining cheese.
Bake – Preheat oven to 375°F (190°C). Bake for 30–40 minutes, or until the center is set and the top is golden.
Rest & Serve – Let cool for 10 minutes, slice into squares, garnish with extra chives, and serve warm.