Creamy, starchy, salty, crunchy, cheesy -- here's plenty of proof that plain white can be every bit as thrilling to the taste buds as it is to the eyes.
Place potatoes in a stockpot; add water to cover, and salt lightly. Bring to a boil; cook until tender when pierced, about 15 minutes. Drain; let cool completely. Refrigerate until ready to assemble, up to 2 days.
Heat cream in a small pan over medium heat, just until simmering. Remove from heat; stir in horseradish. Cover; refrigerate 2 hours or overnight to infuse. Strain into cold bowl; discard horseradish. Refrigerate, airtight, up to 1 day. Just before serving, add creme fraiche and salt. Whisk until medium peaks form. Place in a pastry bag fitted with a small star tip.
Slice potatoes 1/2 inch thick; cut out using a 1-inch fluted cutter. Sprinkle with salt. Pipe on horseradish cream; top with scallions. Chill; serve cold.