Preheat oven to 375ºF.
Cut tops of rolls off.
Place bottom into a greased baking dish.
Spread 3 tablespoons of butter over bottom layer of rolls.
Place 6 slices of cheese on top of butter.
Spread sliced corned beef evenly over top of cheese.
In a small bowl, combine sauerkraut and thousand island dressing.
Spread mixture over top of corned beef.
Add remaining 6 slices of cheese over sauerkraut mixture.
Place roll tops on top of cheese.
Melt remaining butter and brush it over top of sliders.
Sprinkle garlic powder and poppy seeds on top.
Bake for 12-15 minutes or until cheese is melted and tops of rolls are a bit crunchy.
Slice in between rolls with serrated edge knife before serving to make it easier.