In a small bowl, whisk together the sour cream, horseradish, Dijon mustard, lemon juice, salt, and black pepper until well combined.
Taste the horseradish sauce and adjust the seasoning as needed, adding more salt, pepper, or horseradish to taste.
Cover the bowl with plastic wrap and refrigerate the horseradish sauce for at least 30 minutes to allow the flavors to meld together.
When ready to serve, give the horseradish sauce a quick stir and transfer it to a serving dish.
Enjoy your homemade horseradish sauce as a condiment with your favorite meats or as a dip for vegetables.