Authentic Spanish tortilla with sweet potato and kale

Ingredients:

• 8 large eggs, beaten
• 1/4 cup olive oil
• 1 sweet potato, peeled, halved and sliced ​​crosswise
• Half an onion, thinly sliced
• 1 teaspoon coarse salt
• 5 leaves of Tuscan kale, chopped
• 1 and 1/4 tbsp. grated smoked mozzarella

Preparation:

1. Preheat oven to grill mode.
2. Heat an 8-inch cast-iron skillet over medium heat. Add olive oil to the skillet and heat. Add the sweet potato, onion, and 1/4 teaspoon salt. Cook, stirring frequently, until the onion and sweet potato begin to brown and the sweet potato is cooked through, about 8 minutes. Add the kale and sprinkle with 1/2 teaspoon salt. Cook, stirring frequently, until the kale is wilted and tender, about 3 minutes.
3. Sprinkle the eggs with the remaining 1/4 teaspoon salt and stir in 1 cup smoked mozzarella. Pour the egg mixture over the vegetable mixture. Using a rubber spatula, gently fold, ensuring all the sweet potatoes are coated and all the ingredients are evenly distributed. Cook on the stovetop for about 3 minutes until the frittata is set on the bottom. Sprinkle with the remaining 1/4 cup mozzarella.
4. Transfer the pan to the broiler and broil until golden brown, about 3 minutes. Let cool in the pan for 5 minutes. Run a thin knife around the edges of the frittata and cut into 16 squares. Serve warm or at room temperature.