Melt butter in a large saucepan and add onions and celery. Cook on medium heat until the onions are transparent. Add the flour, stirring to coat the onions and celery thoroughly. Continue to cook for an additional 1-2 minutes.
Gradually stir in the milk, stock and spices. Simmer for 4-5 minutes until the liquid begins to thicken. Add the grated cheese and continue to stir. Top with chopped parsley and croutons prior to serving.