Fill a large pot with water and bring it to a boil.
Add potatoes and boil until they are fork tender, about 10 minutes.
Preheat oven to 400 degrees F.
Once potatoes are cooked and have cooled, cut each one in half and cut a small slice off of the rounded end so the potato can sit up on a flat surface.
Scoop out the inside of each potato half saving the potato insides in a bowl.
Add cheese, corned beef, butter to the bowl with the saved potato insides and mix together until well combined. Salt potato mixture to taste. Also, sprinkle some salt over the potato halves.
Scoop mixture into potato halves and then place them on a baking sheet lined with a silicone mat or parchment paper.
Place baking sheet in oven for 10 minutes.
Remove from oven and serve with a dollop of sour cream, if desired.