Warm Spinach Salad with Fried Egg and Potatoes

In a large non-stick skillet, heat 2 tablespoons oil over medium. Add potatoes; cook, tossing occasionally, until potatoes are tender and browned, 12-14 minutes. Meanwhile, in a large bowl, combine remaining 2 tablespoons oil with vinegar, mustard and shallot; season with salt and pepper and whisk to combine. Add spinach and Parmesan (do not toss); set aside. When potatoes are done, transfer to bowl with spinach and dressing (reserve skillet). Toss salad until spinach is slightly wilted, and divide among four plates. Heat skillet over medium, and gently crack eggs into skillet without breaking yolks; season with salt and pepper. Cook until whites are almost set, about 1 minute. Cover, turn off heat, and let stand until whites are just set but yolks are still soft, about 2 minutes more. Top each salad with a fried egg and serve immediately.