Swiss Chard, Leek and Sweet Potato Frittata

Ingredients

• 1 tablespoon olive oil
• 2 tablespoons unsalted butter divided
• 1 pound sweet potato peeled and cubed, about 2 medium
• 1 leek medium, washed and drained
• 1 bunch rainbow chard washed and drained, if required
• 8 large eggs
• 1/3 cup sour cream or milk or milk of choice
• 1/2 teaspoon Dijon mustard
• 1/2 teaspoon dried oregano or 1 tsp chopped fresh
• 1 teaspoon fine sea salt
• 1/4 teaspoon freshly grated nutmeg
• 1/2 teaspoon freshly ground black pepper
• 3/4 cup grated cheddar cheese or cheese of choice, ricotta, Parm, etc