01 - Set the oven temperature to 400°F.
02 - Peel onions and cut each in half from root to tip. Slice each half into wedges, maintaining the root end intact to keep layers together.
03 - Place onion wedges on a baking sheet lined with parchment paper.
04 - Drizzle with olive oil and sprinkle with sea salt, black pepper, and optional thyme. Toss gently to coat evenly.
05 - Roast in the preheated oven for 30 to 35 minutes, turning once halfway through, until golden brown and tender.
06 - Optionally, drizzle balsamic vinegar over onions and roast for an additional 2 minutes.
07 - Serve warm as a side or at room temperature incorporated into salads.