Cut potatoes in evenly sized pieces. Roast in 450 degree oven until browned and just cooked through.
Cook bacon in oven until very crisp.
When potatoes come out pour hot bacon fat from cooked bacon onto the potatoes and toss.
Add chopped bacon, chopped rosemary, mustard, mayonnaise.
Season with salt and pepper to taste.
If it seems a little dry add more mustard and mayonnaise.