Preheat oven to 350 degrees
Cut the top and bottom off each of the onions. Scoop out as much onion as you can while maintaining the shape of the onion and leave enough base to hold the custard later. In essence, make a hole in the middle that will hold 1/2 cup or more of custard. Take the parts you cut out and put them through a food processor.
Coat the hollowed out onions with oil, salt, and pepper. Roast at 350 degrees until well browned and softened, yet maintaining their integrity to stand (about 15 minutes)
Chop the garlic fine. And chop the green onion. Put the green onion aside. Mix the garlic with the chopped innards from the roasted onions. Saute them in a little olive oil. Start at high heat to get some color, then turn down to low to caramelize. Cook until sweet, brown, and not too wet. Set aside.
make the custard filling: Stir together cream and half the sugar in a heavy bottom pot. Bring to a simmer. Meanwhile, Whisk the egg yolks with the cornstarch and1/4 cup of sugar. Slowly ladle the cream mixture into the yolk mix, whisking constantly to prevent curdling the eggs. Use a rubber spatula to return the mix to the pot. Put over low to medium heat, stir constantly until it has thickened. Do not overcook or you will have scrambled eggs. Turn off the heat and stir in the butter, caramelized onion and garlic, and chives. Incorporate them well.
Spoon the Custard mix into the Roasted onion bowls. Sprinkle the top with a thin layer of sugar and run a torch over the top to create a caramel disk on top. Serve immediately.
