If using fresh tomatoes, blanch them first to easily skin them and cut up. If you haven’t blanched before, bring a large pot of water to a boil, gently crop the tomatoes, a few at a time, into the water. It will only take about 30-60 seconds for the them to be ready. Usually the skin splits a little. Remove them and put into a bath of cold water to stop the cooking and to make them easier to handle. Once cooled enough to handle, remove the skins, core them (removing the stem portion) and cut up into chunks.