We use Maris Piper spuds, scrub them, slice them into 8, parboil them for 5 mins then coat them in a tbsp olive oil/ tsp of paprika/ tsp spicey season all/ crushed garlic/ desert spoon of polenta flour (spelling?) and them bake them for 40 mins at 180 in a fan oven but they don't always crisp up....just wondering if I'm doing something wrong?