Preheat oven to 375 degrees F.
Preheat a skillet over medium high heat. Add extra-virgin olive oil, garlic and onions. Sweat them out 2 to 3 minutes then add cherry tomatoes. Turn tomatoes to coat in fat. Add sherry vinegar or sherry, sugar, pepper flakes and salt. Toss to coat tomatoes and roast for 18 to 20 minutes.