Place all of the above in a large soup pot.
Slowly fill with water; amount of water used will be determined by the size of the pot.
Set to low and cover, stirring occasionally, for 4 hours.
Add salt to taste.
Hazelnuts will float to top. Skim off and reserve.
Saute leeks and onions on low in large stock pot until soft.
Add apples and cook 20 minutes. Add stock slowly as onions, apples and leeks cook, seasoning with salt and pepper. When all stock is added, cook for 40 more minutes.
Add thyme, 1 can evaporated milk, a second if necessary, then puree.
Add stock if necessary and add hazelnuts reserved from stock.
Garnish with fresh apple slice.