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, kosher salt, black pepper, dried thyme or rosemary, and minced garlic if using until evenly coated.
03 - Spread the seasoned vegetables in a single layer on the prepared baking sheet, making sure not to overcrowd the pan for even roasting.
04 - Roast for 35 to 40 minutes, flipping the vegetables halfway through, until the potatoes are golden and fork-tender and the onions are deeply caramelized.
05 - Remove from the oven and garnish with freshly chopped parsley if desired. Serve warm as a side dish.