01 - Heat butter or oil in a large nonstick skillet over medium heat.
02 - Add diced potatoes and cook, stirring regularly, until golden and tender, about 10 to 12 minutes.
03 - Add onion and bell pepper, if using. Sauté for 3 to 4 minutes until the vegetables soften.
04 - In a mixing bowl, thoroughly whisk together eggs, milk, salt, and black pepper.
05 - Reduce heat to medium-low. Pour egg mixture over the cooked vegetables in the skillet. Let set undisturbed for 30 seconds.
06 - Gently stir and fold with a spatula as the eggs begin to set, cooking until mostly cooked but slightly runny, about 2 to 3 minutes.
07 - Scatter shredded cheddar evenly over the eggs. Allow to melt for 1 minute, then gently fold to combine as cheese softens.
08 - Slide onto plates and garnish with chives or green onions as desired. Serve immediately.