Heat the soup stock on medium high in a skillet large enough to hold the celery in a single layer.
Add the celery to the skillet and stir to wet.
Sprinkle the flour and salt and pepper overtop and stir a bit til the flour is no longer visible.
Reduce to a slow simmer, cover and let cook til the celery reaches the 'crunch' you like (it will get soft if that's what you want but will take longer to cook), stirring occasionally.