Cook the diced potatoes in lightly salted stock for 4-5 minutes. Add the corn and boil until the vegetables are tender, another 6-8 minutes or so. Strain off the cooking liquid and reserve for the chowder.
Cook the bacon until crisp, using a large saucepan or small kettle. Remove from the pan with a slotted spoon and set aside. Drain off all but 3 tbsp. of the bacon fat. Cook the green pepper, onion, and celery in the reserved fat until lightly colored, about 6-7 minutes. Sprinkle the flour and blend well. Stir in the reserved potato liquid, milk, bay leaf, parsley, salt, pepper, and nutmeg. Bring to a boil and cook for 2-3 minutes. Stir in the potatoes and corn; remove from the heat and let mellow at room temperature for 30-45 minutes.
Remove the bay leaf. Reheat the chowder gently, adjusting seasonings as desired. Stir in the yogurt and reserved bacon at the last minute; heat briefly and serve. Serves 4.