Prepare the onions by rinsing under cold water. Then cut off the stringy root ends and approximately 5 inches of the green tops. This will leave you with most of the onion's white parts to use in the dressing. If you are going to use an immersion blender, just a rough chop of the onions is needed. If you are not using an immersion blender, finely chop the onions by hand.
In a medium sized bowl, combine sour cream, mayonnaise, green onions and lemon juice. Use the immersion blender or a large wooden spoon to mix everything together.
Chop and crumble the blue cheese into small bite sized pieces.
Gently mix the crumbled blue cheese in with the rest of the ingredients. Add salt and pepper to taste.
Special Note About Immersion Blenders:
I used an immersion blender for this dressing because that's the way my Uncle Randy does it. An immersion blender incorporates the ingredients and finely chops the onions really nicely. But an immersion blender is not mandatory! This recipe is just as fantastic when you make it by hand mixing and chopping.