welsh potato, leek and ham soup

Ingredients

• 1 3/4 ounces butter
• 1 tablespoon olive oil
• 2 - shallots, peeled and finely chopped
• 2 - leeks, sliced
• 1 - stalk of celery, finely chopped
• 1-2 clove garlic, peeled and finely chopped
• 2 large or 3 medium potatoes, peeled and dicedsprig of thyme
• 1 - large fresh sprig of thyme
• 1 - bay leaf
• 6 ounces shredded or diced ham hock
• 2 pints good chicken stock
• - a handful of fersh parsley and/or tarragon
• - bread to serve with