Ingredients
1 lb. russet potatoes (about 2 medium)
1 lb. purple potatoes (see Tip)
1 lb. sweet potatoes (about 2 medium)
3 tbsp. unsalted butter
5 medium cloves garlic (finely grated)
3 tbsp. all-purpose flour
3 cup half-and-half
1/2 cup prepared horseradish
Kosher salt (such as Diamond Crystal)
2 cup Cheddar or Gruyère
Directions
- 1
Arrange a rack in the top third of the oven and heat to 400 degrees.
- 2
Peel all the potatoes and cut into 1/8-inch-thick slices with a sharp knife or mandoline.
- 3
Melt the butter over medium heat. Add the garlic and cook until just golden, about 1 minute.
- 4
Sprinkle in the flour and whisk until a paste forms, then continue stirring to cook the flour until bubbling, 30 seconds to 1 minute more.
- 5
Slowly pour in 1 1/2 cups of the half-the-half and whisk until combined. Whisk in remaining half-and-half, the horseradish and 2 teaspoons salt.
- 6
Bring to a simmer while whisking constantly, then turn off heat and let steep for about 5 minutes.
- 7
Ladle 1 cup of the horseradish cream sauce into a 9-by-13-inch baking dish, spreading to fully coat the bottom of the dish.
- 8
Add half the sliced potatoes in an even layer; have fun mixing the colors. Sprinkle half the cheese on top and pour over another cup of the sauce, making sure the sauce is fully covering the cheese and potatoes.
- 9
Add the remaining sliced potatoes, and top with remaining sauce and cheese.
- 10
Cover with aluminum foil and bake until potatoes are almost fully tender and sauce is bubbling, about 45 minutes.
- 11
Remove the foil and continue to bake until the edges are slightly crisp and the cheese is golden brown in spots, about 10 minutes more.
- 12
Let sit at room temperature for 15 minutes before serving.