Pre-heat oven to 350°F. Remove corned beef brisket from the package and place the fat side up on a rack in a pan. Add 1" of water to the bottom of the pan. Spread spices from the packet over brisket, if desired. Brisket is already seasoned. Cover the pan with a lid of foil. Bake for 50 minutes per pound or until fork tender with 10 minutes left; uncover pan and bake at 375°F. Allow to cool for 20 minutes before slicing against the grain.

Preheat oven to 375°F. In a large bowl whisk together eggs, half and half and remaining salt and pepper. Add cheddar cheese and chopped parsley and mix until combined. Set aside.

Heat olive oil in a large, oven-proof skillet over medium heat. Add onion, cabbage, 1/2teaspoon kosher salt and 1/2 teaspoon ground black pepper. Stir to combine and cook until onions have softened and cabbage has wilted, 10-12 minutes.

Add corned beef and potatoes and cook an additional 5 minutes, stirring frequently.Using a spatula, spread mixture into an even layer. Pour egg mixture evenly over cabbage and cook for 5 minutes, undisturbed, until edges begin to set. Transfer pan to preheated oven and bake for 20 minutes or until the middle is set and frittata is puffed and golden.

Let cool 5 minutes before serving. Garnish with fresh parsley.