Step 1Prepare the tomatoes: Bring a large saucepan of water to a boil over high heat. Core the tomatoes, and slit the skin at the bottom of each tomato in an X. Put the tomatoes into the boiling water to cover and boil just until the tomato skin starts to pull away from the X, about 30 seconds. Transfer the tomatoes to a bowl of ice water to stop the cooking. Remove them from the cold water promptly and pull off the peel. Halve the tomatoes and squeeze out their juice and seeds, then chop them. You should have a generous 2 1/2 cups. Set aside.
Step 2Heat the olive oil in a deep sauté pan. Add the diced red pepper and cook over medium-low heat, stirring occasionally, until tender, about 10 minutes.
Step 3Add the garlic, paprika and pepper flakes, and cook, stirring, until fragrant, about 10 seconds. Add the chopped tomatoes, salt and pepper, and mix well. Cover and cook over medium heat, stirring often, until the tomatoes are very tender and the sauce is thick, about 15 minutes. Taste and adjust the seasoning if desired; this makes about 2 cups sauce. Serve hot or at room temperature. Stir before serving.