Heat a medium skillet over high heat. Add the cored tomatoes and cook until they are charred on all sides, about 5 minutes. Remove to the bowl of a food processor fitted with the metal blade.
Let the skillet cool slightly by taking it off the heat or decreasing the heat, depending on how smoking-hot your skillet is. Have the heat at low and add the oil (the skillet will still hold a great deal of heat). Add the onion and garlic, and saute, stirring occasionally, until both are a deep golden-brown, 8 to 10 minutes. Remove from the heat and let them cool slightly. Transfer to the food processor bowl containing the reserved charred tomato, and process until smooth. Transfer the mixture to a large saucepan. Cook over medium-low heat until thickened, 5 to 7 minutes. Season with salt and pepper.
Add the chopped collards and cook until just tender, 15 to 20 minutes. Taste and adjust for seasoning with salt and pepper. Serve warm.
"Lighten Up, Y'all" by Virginia Willis © Ten Speed Press, a division of Penguin Random House, Inc. 2015. Provided courtesy of Virginia Willis. All right reserved. Photography © 2015 by Angie Mosier.