Step 1

Preheat the oven to 350°F. Butter an 8x8 baking dish.

Step 2

Parboil the potatoes: Scrub the potatoes clean, but leave the skins on. Place them in a large pot and cover with water. Bring to a boil. Allow to boil for about 10 minutes.Turn off heat and let the potatoes sit in the hot water for another 10 minutes. When ready, you should be able to pierce the potatoes with a fork, but still feel slight resistance. Drain the potatoes and set aside until cool enough to handle.If making the potatoes ahead, cool to room temp, cover, and store in fridge for up to 3 days.

Step 3

Meanwhile, cook the onions and peppers: In a medium skillet, melt 5 tablespoons butter, cook the onions and bell pepper until the onions are soft and translucent, about 6 minutes. Set aside.

Step 4

Peel and shred the potatoes: Once the potatoes are cool enough to handle, score them along their equator with a paring knife. Twist each side in opposite directions to remove skin. The skin should pull off easily. If any bits of skin remain, trim them off with a knife.Shred the potatoes using a food processor fitted with the shredder disk, or shred them by hand using the large holes on a cheese grater.

Step 5

Assemble the casserole: Transfer shredded potatoes to a large bowl, and mix with the cooked onions, pepper, cream of chicken soup, cheddar cheese, sour cream, 1 teaspoon of salt, and pepper.Stir until thoroughly combined. Spread into casserole dish.

Step 6

Toast the breadcrumbs: In the same pan where you cooked the onions, melt remaining 3 tablespoons of butter over medium heat. Add the panko and remaining 1/4 teaspoon of salt. Stir to coat.Toast panko, stirring frequently, until it takes on a golden hue, about 5 minutes. Sprinkle evenly over the top of the potatoes.

Step 7

Bake at 350°F for 45 minutes. When done, the potatoes should be bubbling around the edges, and the panko top will be golden.

Step 8

Cool for 10 minutes, then spoon onto plates.