01 - Preheat oven to 425°F. Line a large baking sheet with parchment paper.
02 - In a large bowl, toss potatoes and onions with olive oil, salt, pepper, thyme or rosemary, and garlic if using until evenly coated.
03 - Spread the seasoned vegetables in a single layer on the prepared baking sheet, making sure not to crowd the pieces.
04 - Roast for 35 to 40 minutes, flipping halfway through, until the potatoes are golden and tender and the onions are caramelized.
05 - Remove from oven and garnish with fresh chopped parsley if desired. Serve warm.