1. Prep, 15 minutes; Cook, Auto/Low 8 hrs or High 4 hours; THEN Auto/Low 8 hrs or High 4 hrs
2. Preheat the slow cooker, if required. Sit the ham and bay leaf in the slow cooker and cover with 3 cups of water. Cover and cook on auto/low for 8 hours or on high for 4 hours, then remove the ham and set aside. Discard the stock, or strain and reserve a little to add to the soup. 
3. Heat the oil in a large heavy-based pan over medium heat, add the onion, and cook for 3-4 minutes until soft. Season with salt and pepper, then stir in the mustard, garlic, and herbs (reserve some thyme leaves for garnish). Add a little stock and bring to a boil, then add in the peas (if you prefer pureed, pulse them gently in a food processor or use an immersion blender). Transfer to the slow cooker, add the remaining stock and the potatoes, cover, and cook on auto/low for 8 hours or on high for 4 hours. Remove any fat from the ham, chop into bite-sized pieces, and stir into the soup. Taste and season as needed. Garnish with reserved the thyme leaves and serve with whole grain bread.

Traditional method: 

1. Prep, 15 minutes; Cook, 2 hrs
2. Add the ham and bay leaf to a large pan, cover with 1 quart of water, and bring to a boil. Partially cover, reduce to a simmer, and cook for about 1 hour or until the ham is cooked. Skim away any scum that comes to the surface of the pan as you go. Discard the stock, or strain and reserve a little to add to the soup. Set the ham aside until cool enough to handle. 
3. Heat the oil in a large heavy-based pan over medium heat, add the onion, and cook for 3-4 minutes until soft. Season with salt and pepper, then stir in the mustard, garlic, and herbs (reserve some thyme leaves for garnish). Add a little stock and bring to a boil, then add in the peas and remaining stock. Bring to a boil, reduce to a simmer, and cook for 45 minutes, topping up with hot water as needed. 
4. About 20 minutes before the end of the cooking time, bring a separate pot of water to a boil. Add the potatoes, bring back up to a boil, and then simmer for 12-15 minutes until soft. Drain and set aside. Remove the rosemary from the soup, then use an immersion blender to gently puree the peas, or ladle them into a food processor and pulse a couple of times. Return them to the pot and stir in the potatoes. Remove any fat from the ham, chop into bite-sized pieces, and stir into the soup. Taste and adjust seasoning as needed. Garnish with the reserved thyme leaves and serve with whole grain bread. 
5. Freezes for 3 months.