Preheat oven to 425 degrees, with racks in upper and middle thirds. On a rimmed baking sheet, toss potatoes and garlic with 1 tablespoon oil; season with salt and pepper. Arrange in a single layer on sheet and roast on middle rack until potatoes are golden and crisp, about 25 minutes, stirring halfway through.
Meanwhile, in a medium bowl, whisk together eggs and sour cream and season with salt and pepper. In a 10-inch cast-iron skillet, heat 1 tablespoon oil over medium. Add onion and green beans and cook, stirring occasionally, until beans are tender, about 10 minutes. Add broccoli and tomato, and season with salt and pepper. Add egg mixture and stir to combine. Sprinkle with Parmesan and cook, undisturbed, until edge is set, about 2 minutes.
Transfer skillet to upper rack in oven and bake until slightly puffed and almost set, about 8 minutes. Heat broiler and broil until cheese is browned and bubbling, about 1 minute. Run a rubber spatula around edge of frittata and transfer to a plate. Cut into wedges and serve with potatoes and garlic.
$1.98 per serving