Clean quahogs under cold water and add to boiling water.
Once quahogs have opened, remove from pot and allow quahogs to cool. Remove meat from shells and mince. Reserve the water (quahog stock) that the quahogs were in and keep hot.
In another covered pot, cover potatoes in cold water and bring to a boil until fork tender.
In another pot, melt butter over medium heat. Add onions, lower heat and cook about 20 minutes or until the onions are soft. Stir in flour and cook roux for another 10 minutes. Add reserved quahog stock and minced quahog meat. Bring to a low boil to thicken. This is the quahog chowder base. (Now is a good time to cool and freeze some of this stock for a later use. Don’t add the potatoes, as they don’t freeze well.)
Add potatoes, half and half and heat. Season with salt and pepper and serve.