Step 1

Place the potato cubes into a large pot and cover with salted water. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until tender, about 25 minutes. Drain and allow to steam dry for a minute or two.

Step 2

Melt 1/2 cup of butter in a large skillet over medium heat, and cook and stir the onions and celery until they are reduced and browned, about 30 minutes.

Step 3

Preheat oven to 350 degrees F (175 degrees C). Grease 2 glass baking dishes, each 9x13 inches.

Step 4

Place another 1/2 cup of butter into the work bowl of a stand mixer, and add the cooked potatoes. Start the mixer on Low setting. While mixer is running, pour in 1 cup of milk, and add 1 tablespoon of seasoned salt and 4 slices of torn bread. Mix those ingredients briefly into the mixture, and pour in 1/2 cup of milk and 4 more bread slices. Mix that addition, and then mix in 2 more bread slices.

Step 5

After the last 2 bread slices have been roughly incorporated, place another 1/2 cup of butter, 1 tablespoon of seasoned salt, all the onions, celery, and butter from the skillet, and 4 more slices of bread into the mixer bowl. Mix to incorporate, and finally mix in 2 to 4 additional torn bread slices. Allow the mixer to run until the dressing is the desired consistency.

Step 6

Place half the dressing into each prepared baking dish, and top the dressing with the remaining 1/2 cup of butter, cut into thin slices and scattered over the top. Sprinkle remaining 1 tablespoon of seasoned salt evenly over the top of the dishes. Cover the dishes with aluminum foil.

Step 7

Bake in the preheated oven until the dressing is browned, about 1 hour.