Beat the egg in a blender or food processor for 30 seconds on its own. A stick blender would also work.
Add the lemon juice, water, and mustard and process for 30 more seconds.
Gradually pour in the olive oil in a slow stream while blending until the mixture is emulsified into a thick mayonnaise.
To Make The Ranch Seasoning
Combine the dried dill, dried parsley, garlic, and onion powder. Add a pinch of salt and pepper.
To Make The Ranch Dressing
In a mixing bowl or jar combine 1 cup of the mayonnaise with the sour cream, ranch seasoning, and a pinch of salt. Mix well, and if possible, allow the flavors to develop for 10-15 minutes, covered in the fridge. Serve cold.