Using a blender, food processor, or immersion blender in the can, pulse the tomatoes until mostly pureed with some small pieces of tomato still intact, like a not-too-chunky salsa.
Heat oil in a large pot over medium heat (the pot is going to seem much too big, but this sauce likes to splatter and the larger pot will cut down on cooking time). Add garlic and cook until browned and fragrant, about 30 seconds. Add pureed tomatoes (the oil will sizzle and splash when you add tomatoes, so do so carefully), sugar, and basil. Stir and bring to a simmer.
Simmer uncovered* for 20-30 minutes (your cooking time will very greatly depending on the size of your pot and type of tomatoes), stirring occasionally, until sauce is thickened and has reduced down to about 1 1/2 cups.