Peel and chop up the potatoes and onion, then melt butter in a saucepan.
When butter is melted, add potatoes, onions, and salt to the pan and stir to mix. Cover and let it simmer for about ten minutes, stirring occasionally, making sure that the potatoes and onions are well-coated in butter.
Add the stock and bring to a boil, then let it simmer for twenty minutes.
Remove the pan from the stove and allow it to cool a bit, then puree with a stick blender.
Add shredded cheese to the top (we like a LOT) and garlic salt to taste.
Serve immediately!
Notes
I've found that Yukon golds work really well in this recipe, but you can also use plain old Russets.Adapted from Irish Traditional Cooking