Peel and thinly slice potatoes. Set aside
Microwave water to bring it to a boil. Add salt to the water, and set aside
Melt butter, and set aside.
In a 5-7 quart slow cooker, layer potatoes and pour boiling salted water over the top.
Brush the top layer of potatoes with 3 Tablespoons of melted butter.
Cover with a piece of parchment paper, being sure to firmly press the parchment over the top of the potatoes.
Cover and cook until potatoes are tender, 5-6 hours on low or 3-4 hours on high.
After potatoes are fork tender, remove and discard parchment.
Mash the potatoes with a potato masher until smooth.
Stir in remaining 9 tablespoons of butter, sour cream, and softened cream cheese.
Taste, and season with salt and pepper.
Stir in chives, and serve.