Spray a pan with oil and place the celery in the pan. Place the pan over medium heat.
When the pan heats up and the celery begins to sizzle reduce the heat to medium low and cover. Cook the celery for about 20 minutes. Toss frequently.
Place the water in a large stock pot over high heat.
Quarter the potatoes and add to the stock pot. Cover with water by about an inch. Bring to boil and then reduce heat until the water is simmering.
Cook the potatoes about 15 – 20 minutes until slightly soft in the middle. They should give when squeezed.
Remove from heat and drain water.
Place the butter, buttermilk, milk, salt and celery in a blender. Puree until smooth.
Add the celery mixture to the potatoes and mash potatoes until creamy.
Be careful because over mashing will result in pasty potatoes. Add ground black pepper to taste and serve.
