Bake until edges of potatoes are starting to brown and crisp, about 20 minutes. Meanwhile, in a small bowl, stir mayonnaise, ketchup, and Cajun seasoning until smooth. Leave bacon in oven ...
The potatoes don’t roast in this oil, so much as braise: they will crisp up in parts, but mostly just become softened and rich in the sweet peppery juices. Preheat the oven to 220C/200C Fan/Gas 7.
Remove from oven and carefully, with the bottom of a heavy glass, smash each potato to 1/4 inch thickness. Return to oven and cook until crispy, about 15-20 minutes. Serve with dip.