roasted onions with pesto

http://www.tastingtable.com/entry_detail/chefs_recipes/8010

6 tennis-ball-size young red onions (preferably the kind with the green tops still attached)
Flaky sea salt
½ cup plus 3 tablespoons extra-virgin olive oil, divided, plus more if needed
2 cups sage leaves
½ medium garlic clove, roughly chopped
3 tablespoons pine nuts
5 tablespoons finely grated Parmigiano-Reggiano cheese (about 1 ounce)

DIRECTIONS 1. Preheat the oven to 350°. If using young onions with the greens still attached, trim the greens to within ½ inch of the onion. Peel the onion and trim the root without completely cutting it off (the root end keeps the onions intact while roasting). Halve the onions lengthwise and place in a large bowl with 4 large pinches of salt.
2. In a wide heavy-bottomed oven-safe skillet or flame-safe baking dish, heat 3 tablespoons of the oil over high heat until the oil begins to smoke, 2 to 3 minutes. Reduce the heat to medium and carefully add the onions cut-side down to the pan (they should fit in a snug single layer). Cook, using tongs to peek under the onions occasionally, until you see spots of golden brown, 8 to 12 minutes.
3. Place the pan in the oven and cook until the cut sides of the onions are deep golden-brown (without any black spots), about 30 minutes. Remove the pan from the oven and use tongs to turn the onions over. Increase the temperature to 450° and continue to cook until the onions are very soft but not falling apart, 10 to 15 minutes longer.
4. Meanwhile, make the sage pesto: In the bowl of a food processor, pulse the sage, garlic, pine nuts, Parmesan cheese and 4 large pinches of salt until roughly chopped. Add just shy of ½ cup of oil and run the processor, stopping to scrape the sides of the bowl as needed, until the mixture is well combined but still chunky (add more olive oil as needed). Taste and season with more salt if needed.
5. Remove the onions from the oven and arrange on a plate. Add a few dollops of sage pesto and serve.