Heat the olive oil and butter in a large pot or Dutch oven set over medium-low heat. Add the onions and garlic and cook, stirring occasionally, for 6-8 minutes, until the onions are translucent and just starting to lightly brown. If brown bits form on the bottom of the pan, use a spatula to scrape them up and stir them into the vegetables.
2 tablespoons extra virgin olive oil, 2 tablespoons unsalted butter, 2 cups chopped yellow onion, 4 large or 5 medium cloves garlic
Stir in the tomato paste followed by the tomato puree, vegetable stock, sugar, salt, pepper, basil, oregano, and crushed red pepper. Bring to a simmer over high heat, then turn the heat to low and cover. Simmer for 45 minutes.
2 tablespoons tomato paste, 56 ounces tomato puree, 1 cup vegetable stock, 1 tablespoon granulated sugar, 1 teaspoon fine sea salt, 1/2 teaspoon ground black pepper, 3/4 cup packed fresh basil, 1/2 teaspoon dried oregano, 1/4 teaspoon crushed red pepper
Remove the cover and allow the liquid to cool for several minutes, then carefully ladle it into a blender and puree, in batches if necessary. Return to the pot and stir in the cream. Taste; add more salt and pepper if desired.