In a mixing bowl, add 1 cup of sour cream and 1/4 cup of prepared horseradish. Mix well using a whisk until smooth.

Stir in 2 tablespoons of Dijon mustard and the juice of half a lemon. Add salt and black pepper to taste and mix until thoroughly blended.

Taste the sauce and add more horseradish if desired, mixing until incorporated.

Cover the bowl with plastic wrap or transfer the sauce to an airtight container and refrigerate for at least 30 minutes.

Serve the chilled sauce in a decorative bowl, garnished with chopped chives or parsley if desired.