Marinate the chicken: Pat the chicken dry thoroughly with paper towels. In a large bowl, combine 3 tablespoons olive oil, oregano, thyme, paprika, garlic powder, cumin, 1 teaspoon salt and black pepper. Add the chicken and toss until evenly coated. Cover and refrigerate for at least 1 hour, or up to overnight.
Preheat the oven: Preheat the oven to 425°F (220°C).
Prepare the potatoes: Place potatoes in a large roasting pan or rimmed baking sheet. Add the remaining 2 tablespoons olive oil, ½ teaspoon salt and leaves from 1 rosemary sprig. Toss well to coat.
Assemble: Arrange the potatoes in a single layer. Add the onion and unpeeled garlic cloves, then arrange the chicken between the potatoes, skin-side up. Scatter the remaining rosemary over the pan.
Roast: Roast for 50–60 minutes, or until the chicken is deeply golden and cooked through and the potatoes are tender and browned. The thickest part of the chicken should register at least 165°F (74°C).
Serve: Let rest for 5 minutes, then serve warm with the roasted potatoes, onions and garlic.
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Notes
Best potatoes: Yukon Gold, red potatoes or other roasting potatoes work especially well because they become creamy inside while browning nicely.
Cut evenly: Keep the potato pieces roughly the same size so they cook at the same rate. If using very large potatoes, cut them into smaller chunks rather than simply quartering them.
Garlic: Roasting the cloves in their skins keeps them from burning. Once cooked, squeeze the soft roasted garlic from the skins and serve alongside the chicken.
Marinating: One hour adds good flavor, but you can marinate the chicken overnight for an easy make-ahead dinner.
No time to marinate? You can roast the chicken immediately. It will still be delicious, although the seasoning won't penetrate quite as deeply.