Preheat grill. Toss potatoes with 1/4 cup olive oil and season with salt and pepper to taste. Grill cut side down for three minutes. Turn and continue grilling two to three minutes. Place in a large bowl.

Place a medium skillet on the side burner or the grill and heat until almost smoking. Add the bacon and cook until golden brown and crisp. Remove to a plate lined with paper towels. Let cool and crumble.

Remoove all but two tablespoons of the bacon fat from the skillet. Add the onions and cook until soft, five or six minutes. Add 1/4 cup olive oil, vinegar, and sugar and cook until sugar is dissolved. Pour the onion mixture over the potatoes, add the crumbled bacon and parsley and toss to combine. Season with salt and lots of black pepper. Spoon the salad onto a large platter and sprinkle with the crumbled blue cheese.