Over medium high heat, begin to cook sausage in a dutch oven. Add potatoes and garlic, stir well and cover. Reduce heat to medium and cook for about 10 minutes, until the potatoes are soft and the sausage is brown. Add spinach and cook for a minute or two more.
While the sausage and potatoes are cooking, mix the eggs and milk in a medium sized bowl.
Turn the heat down to low, add the egg mixture to the dutch oven and top with cheese and salt and pepper. Add salt and pepper to taste, cover the dutch oven, and cook for 15-20 minutes, until the eggs are cooked.
Run your spatula around the edge of the frittata about midway through the cooking time.
Garnish with fresh chives and enjoy!