Preheat the oven to 375 degrees. Coat a baking sheet with olive oil cooking spray.
Cut the onion in half then remove the out layer of skin.
Cut each onion into 4 wedges (or 8 wedges if they are large onions).
Place the onions on the baking sheet and drizzle with some olive oil.
Season well with sea salt and freshly cracked pepper, to taste; toss to coat evenly. Add a couple of sprigs of thyme on top of the onions.
Place into the oven and roast for 20 minutes.
Flip the onions and continue to roast for another 20-25 minutes, or until caramelized and tender.
Remove from the oven and cool. Store in an airtight jar and use with eggs, potatoes, sandwiches, or pasta dishes. Enjoy.