Potato Help

[Sundae]

Please help me Cellar.

I am totally worthless at cooking potatoes in the oven.
I don't mean baked potatoes - I got them.
I mean roast potatoes, or crispy potato cubes, or wedges.

No matter what I do, they stick to the bottom, and I end up with something like scrambled potatoes.

I am in the middle of cooking potato wedges EXACTLY following a recipe online, because I'm tired of the sorry mess in the dish and on my plate. Just gone to turn them over, expecting them to be nice and crispy on one side and found as always, they are stuck to the pan. Forget nice crispy skins as in the picture, I will have the insides on show and no chance of eating the half mash result stuck to the bottom.

What am I doing wrong?
Not enough fat? Too much? Oven too low? Oven too hot?
These I parboiled, then sprayed with oil. I tossed them to ensure all were coated. Into a 200 degree oven as per recipe, turn halfway through.

Once I would simply shrug off. But every time?
I must be making a fundemental error.
Any advice on what it is would be welcome.
All I really want is that none of my potatoes, whatever the size or shape, get stuck to the bottom. I want crispy potatoes like everyone else, damnit!

Please help.