Preheat oven to 400 degrees F.

Heat 1 tablespoon of the oil over medium heat in a 10-inch ovenproof and nonstick skillet. Add the potatoes, season with a pinch of salt and pepper, and saute until golden brown and tender, about 10 minutes. Remove potatoes and set aside.

Add the remaining 1 tablespoon oil to the skillet and add the garlic and kale and season with a pinch of salt and pepper. Saute until kale is wilted, about 5 minutes. Add potatoes and mustard; stir to combine. Stir in beaten eggs and cheese. Place the skillet in the oven. Bake for 20 minutes or until the eggs are cooked through and a toothpick inserted in the center comes out clean.

Once the frittata is finished, run a knife around the edge of the skillet and gently slide the frittata onto a carving board or serving plate. Garnish with additional pecorino cheese if desired. Slice and serve.