How to make it
Heat oil in medium saucepan over medium heat. Add shallots and garlic and sauté until shallots are soft and translucent, about 5 minutes. Add diced tomatoes, sugar, vinegar, salt, and black pepper.
Cook over medium heat until almost all liquid evaporates and mixture is reduced to about 2¼ cups, stirring often, about 30 to 45 minutes. Taste for seasoning and adjust if necessary. Cool before using.