- Preheat the oven to 375°F (190°C). 
- In a skillet, heat olive oil over medium heat. Add the diced potatoes and turnips. Cook until tender and slightly golden, about 8-10 minutes. 
- (Optional) Add diced onions and garlic to the skillet and sauté until softened, about 2-3 minutes. 
- In a mixing bowl, whisk together eggs, milk (or cream), salt, and pepper. 
- Pour the egg mixture over the cooked vegetables in the skillet. Stir gently to combine. 
- Sprinkle shredded cheese and fresh herbs (if using) over the top of the frittata. 
- Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the eggs are set and the top is slightly golden. 
- Remove from the oven, let it cool for a few minutes, then slice and serve.