1. Preheat oven to 350 degrees F.
2. In a large bowl, lightly beat eggs until combined. Add milk, salt and pepper to taste. Set aside.
3. Heat olive oil in a cast iron skillet over medium high heat. Add garlic and cook until fragrant, about 1-2 minutes. Add sweet potatoes and onion and cook, stirring occasionally, until the potatoes have softened and onions have caramelized, about 8-10 minutes. Add kale and cook, stirring occasionally, until wilted, about 2 minutes. Add egg mixture and tomatoes, and cook until the eggs start to set, about 3-4 minutes. Sprinkle with mozzarella.
4. Place into oven and bake until the top is set and cheese has melted, about 10 minutes.
5. Slice the frittata into wedges and serve immediately.
Want more frittata? Check out Chung’s other recipe for “Clean Out the Fridge” Veggie Frittata.