1. Preheat oven to 400°F.
2. Halve or quarter the potatoes so they are bite-sized. In a large bowl, toss together potatoes, onion, olive oil, salt and pepper.
3. Spread out on a large sheet pan and roast for 35 to 45 minutes, until golden and cooked through.
4. Meanwhile, slice the bacon into small strips. Cook the bacon until crispy. With a slotted spoon, remove bacon pieces from the pan and place them on a plate lined with a paper towel.
5. In a large bowl, gently combine the roasted potatoes and onion, sour cream, blue cheese and most of the bacon and green onions, reserving just a bit to garnish. Carefully toss to coat. Taste and add more salt and pepper, if necessary.
6. Sprinkle the remaining bacon and green onions over the top and serve.