Sauté the onions in hot butter, add the pear pieces and sauté for about 3-4 minutes. Then add the potato cubes and deglaze with the stock. Simmer over medium heat for about 20 minutes until the potatoes are tender; puree. Then stir in the cream.
Season with salt, pepper and possibly Williams pear, simmer gently for another 10 minutes.
Season to taste, season if necessary and serve garnished with croutons.