Stir together the short ribs and the reserved sauce, and season the mixture well with salt and pepper to taste.
Working with a few wonton wrappers at a time (keeping the others covered with plastic wrap), moisten the edges with water. Mound 1 scant tablespoon of the filling in the center of each wonton and press another wonton wrapper on top. Press out the air and press the edges very tightly to seal. Transfer to a flour-dusted sheet pan and cover with plastic wrap. Repeat with the remaining wonton wrappers and filling. (The ravioli may be frozen at this point and kept tightly wrapped in the freezer for up to 1 month. Freeze flat on a sheet pan and, when solid, transfer to an airtight container.)
Bring a large pot of water to a simmer and add several hefty pinches of salt. Heat the tomato sauce. Add the ravioli to the simmering water and cook until just tender, about 5-6 minutes. (If frozen, the ravioli will take a few minutes longer.) Drain well and transfer to warmed pasta bowls. Spoon some of the tomato sauce on top of the ravioli and top each portion with some of the grated cheese and shredded basil.
For the Garlicky Tomato Sauce:
Heat the oil in a saucepan over medium heat; add the onion and cook, stirring occasionally, until softened, about 5 minutes. Add the garlic and cook, stirring for 1 minute. Empty the canned tomatoes into a large bowl and use your hands or a clean pair of kitchen shears to chop the tomatoes. Add the chopped tomatoes and juices to the saucepan. Bring the mixture to a boil, turn down to a simmer and simmer for 20 minutes, stirring occasionally, until thickened, about 20 minutes. Stir in the hot red pepper flakes and add salt and pepper to taste.
Makes about 2 cups.