Work in a well-ventilated room backyard or balcony.
Peel horseradish and dice into 1 cm cubes, in a food processor or high-speed blender process until well grounded, season with salt and drizzle with lemon juice or vinegar. If it is to hart to ground add some water, 1 tbsp at the time.
You can stop there or split grounded horseradish in half; in one half add mayonnaise and sour cream and mix well.
If it is still too strong for your taste, add more sour cream.
Put horseradish sauce in an airtight container and store in the refrigerator.