¼ cup (½ stick) unsalted butter
10 sprigs thyme, tied together
1 medium onion, thinly sliced
2 garlic cloves, thinly sliced
¼ cup tomato paste
2 28-oz. cans whole tomatoes
1–2 teaspoons sugar, divided
¼ cup (or more) heavy cream
Kosher salt and freshly ground black pepper