Place a rack in the center of your oven and preheat to 425°F. Line a large rimmed baking sheet with parchment paper.
Halve each onion through its stem ends. Trim off the tip of each stem and remove the peel. Cut each half lengthwise into 3/4- to 1-inch wedges (you will have about four wedges per half). Place in the center of the baking sheet.
Whisk together the remaining ingredients in a small bowl. Pour the oil mixture over the top and gently to coat the onions evenly. Some of the wedges will fall apart, which is fine. Spread into a single layer so that the cut sides of the wedges are touching the sheet pan.
Roast onions for 25 to 35 minutes, until the onions are tender and lightly charred at the edges, using a spatula to flip them once halfway through. Season with a pinch of additional salt. Enjoy warm or at room temperature.
Notes
TO STORE: Refrigerate leftovers in an airtight container in the refrigerator for up to 4 days.
TO REHEAT: Reheat roasted onions in a 350 degree F oven until warmed through, in a nonstick skillet set over medium-low heat, or in the microwave.
TO FREEZE: Freeze leftovers in an airtight container or zip-top freezer bag for up to 2 months. Thaw overnight in the refrigerator, then reheat as directed above.