Thousand Island Dressing with Homemade Mayo

1.) For the homemade mayo, add the room temperature whole egg, 1/2 lemon juice, Dijon mustard, and salt to a large mason jar. Then pour 1 cup of avocado oil (or other specified oil) into the jar and blend with an immersion blender until thick and creamy, which takes about 10-15 seconds.
2.) For the thousand island dressing, combine 3/4 cup of the prepared mayo and all remaining ingredients (1/4 cup ketchup, 2 tbsp finely diced red onion, 2 tsp finely diced pickles, 1 tbsp parsley, the remaining 1/2 lemon juice, 1 tbsp Worcestershire sauce, 2 tbsp sour cream, and 1-2 tsp horseradish) into a large mason jar. Shake vigorously until smooth and well combined.