If you don't have a food mill you have to remove the skins and seeds. Fill a large bowl with ice water and set it close to the stove. Bring a large pot of water to boil. Using a slotted spoon lower the tomatoes into the boiling water for 1 minute to loosen the skins. Remove the tomatoes and plunge them into ice water, letting them cool enough to handle. Using a paring knife, cut and discard cores and skins. Cut tomatoes in half crosswise and discard the seeds. Cut large tomatoes into wedges.
Place the tomatoes in a large heavy bottomed saucepan and add 1/2 c. water. Cover and cook on medium heat, stirring frequently until completely softened for 15-20 minutes. Lower heat if they start to scorch but DO NOT add water. Remove from heat and let cool, stirring occasionally for about 15 minutes.
Puree in batches in blender or food processor until just smooth- if you do too much they will get foamy, which isn't a huge problem but is annoying. Transfer to large clean pot and reheat gently, uncovered, over low heat. If soup is too thin, let it simmer 10-15 minutes.
Season with salt and pepper. If it is too acidic add 1tsp. sugar and taste again before adding more. If you are not serving immediately let cool at room temp and either refrig (up to 5 days) or freeze (up to 6 months). Serve with parm or parm croutons.