Vichyssoise

2 leeks, chopped
1 onion, chopped
2 tablespoons unsalted butter
3/4 cup thinly sliced potatoes
2 1/3 cups chicken stock
salt to taste
ground black pepper to taste
1 1/8 cups heavy whipping cream 

1. Gently sweat the chopped leeks and the chopped onion in butter or margarine until soft, about 8 minutes. Do NOT let them brown.

2. Add potatoes and stock to the saucepan. Salt and pepper to taste; do not overdo them! Bring to the boil, and simmer very gently for 30 minutes.

3. Puree in a blender or food processor until very smooth. Cool. Gently stir in the cream before serving.