Melt butter in a large saucepan over medium heat. Stir in the onion, celery and carrots and saute for 5 minutes. Add the mushrooms and saute for 2 more minutes. Then add the flour and stir well. Gradually pour in the chicken stock, stirring constantly, until all has been added. Bring just to a boil, reduce heat to low and let simmer.
Next, add the rice, chicken, salt, curry powder, mustard powder, parsley, ground black pepper, almonds and sherry. Allow to heat through, then pour in the light cream. Let simmer for 1 to 2 hours. (Note: Do not boil or your roux will break.)