3/4 pound fingerling or other small potatoes, cut into 1/2-inch-thick pieces
Coarse salt and freshly ground pepper
1/4 cup chopped mixed fresh herbs, (such as parsley, rosemary, thyme, and sage), plus more for garnish
10 large eggs
8 ounces fontina cheese, grated
Preheat oven to 375 degrees. Heat oil and butter in a 10-inch ovenproof nonstick skillet over medium heat. Add potatoes; season with salt and pepper. Cook, stirring occasionally, until potatoes are tender and golden brown, 12 to 15 minutes. Stir in herbs.
Meanwhile, whisk the eggs in a medium bowl; season with salt and pepper. Stir in the cheese; pour mixture over potatoes. Stir until eggs begin to set slightly, about 30 seconds. Without stirring, continue cooking until eggs are set on the sides and bottom, about 2 minutes. Transfer skillet to oven; bake until just set, 12 to 15 minutes.
Slide frittata onto a serving platter, or let cool and slide into a 10-inch pie plate (and cover with a second pie plate) for easy transport. Serve garnished with chopped herbs if desired.