Preheat the oven to 400°F (200°C).

Trim the leafy tops from 4 small red beets (about ½ lb total). Wrap the beets in foil (together or individually) and place the foil packet on a baking sheet.

Roast the beets until tender when pierced with the tip of a knife, about 45–60 minutes depending on size. Remove the baking sheet from the oven and let the beets cool inside the foil until cool enough to handle.

Unwrap the foil, peel the cooled beets, and cut them into bite-sized cubes. Set aside.

While the beets roast (or after), place 1 lb small yellow potatoes in a pot and add enough cold water to cover them by about 1 inch. Add kosher salt to the water.

Bring the pot to a boil over high heat, then reduce the heat to medium-low, cover, and simmer until the potatoes are tender when pierced with a knife, about 15 minutes. Drain the potatoes and let them cool until warm or room temperature. Peel them if desired and cut into bite-sized pieces (cube larger potatoes so pieces are similar in size to the beets).

In a serving bowl, stir together ½ cup sour cream, 1 tablespoon mayonnaise, 1 teaspoon prepared horseradish sauce, and 2 tablespoons chopped fresh dill. Season the dressing with kosher salt and freshly ground black pepper to taste.

Gently fold the cubed beets and potatoes into the dill dressing until evenly coated.

Cover the salad and refrigerate for at least 20 minutes (or up to 24 hours) to let flavors meld. When ready to serve, garnish with additional chopped dill and adjust salt and pepper if needed.