4 ounces of smoked chorizo sausage, finely chopped
8 scallions (1 big bunch) trimmed and thinly sliced
8 ounces sharp cheddar cheese, grated
1 cup whole milk Greek yogurt whisked with 1/4 cup of water
2 teaspoons salt
1/2 teaspoon black pepper
1 teaspoon mild smoked paprika
Panko Parmesan Topping:
2 tablespoons unsalted butter
1 cup Panko breadcrumbs (Japanese bread crumbs)
1⁄2 cup freshly grated Parmesan cheese
Add potatoes to a large pot of boiling water. Boil for 30 minutes. Cool potatoes in the fridge for at least two hours or as long as two days.
Make The Panko Topping: Melt the butter in a microwave safe bowl or in a small saucepan. Stir in the panko and parmesan. Toss well, to coat. Set aside.
Preheat oven to 350ºF. Oil or butter a 9-by-13-inch baking dish. Grate the potatoes into a large bowl using the largest holes on a box grater or the shredding disc on your food processor. No need to peel the potatoes. There are lots of nutrients in the skin. Remove any large pieces of skin that don’t make it through the grater.
Heat olive oil in a large heavy skillet. Add onion, pepper, garlic and chorizo. Sauté over medium-high heat for 7 minutes or so until the vegetables have softened and the chorizo is just starting to brown. Scrape vegetables and chirozo into the bowl with the potatoes. Let the mixture cool for a few minutes and then add scallions, cheddar, yogurt, paprika, salt and black pepper. Toss to combine and spread mixture evenly into prepared casserole dish. Sprinkle the Panko topping evenly over the casserole.
Bake for 35-45 minutes, uncovered, until it the casserole is golden brown and heated through.
MAKE THIS AHEAD: To make ahead, follow the instructions through step 4. Cover the casserole with foil or plastic wrap and refrigerate overnight. Before baking, let the casserole sit at room temperature for 20 minutes or so. Bake for 45 minutes, uncovered until golden brown and heated through.