Preheat oven to 425 °F and line two 9 x 13 pans with parchment paper
Wash and stem the cherry tomatoes (or wash and core the whole tomatoes). Spread the tomatoes evenly over two baking pans lined with parchment paper. Toss the onion, garlic cloves and red peppers between the tomatoes so you have even amounts on both pans. Drizzle with the olive oil and season with salt and pepper.
Roast for 35-45 miniutes (approx.). The vegetables will smell amazing as they roast and once done, all the vegetables should be slightly charred around the edges with a deep, roasted color. If you prefer a thicker sauce, cook the vegetables longer but make sure you stir them to keep them from burning. Remove the pans from the oven and let cool 15 minutes.
Place a large colander inside a large bowl and dump the pans into the colander to strain out the juice. Set the juice aside.
Scoop the vegetables into a blender or food processor. Add basil leaves (start with a few and then add to suit your tastes). Puree until the sauce reaches your desired consistency and then add the reserved tomato juice back in, pulsing to combine.
Season with additional salt and pepper, add tomato paste if you wish and stir.
Use immediately over pasta or as part of a pasta dish. If freezing, place in plastic containers or bags for up to 6 months in your freezer.