Mashed potatoes: cook 'em then throw 'em.

A picture would help:) The fix would depend on wood hood vs metal hood.

Lawrence, I find application of mashed potatoes is more effective with a grout bag (or pastry bag, if that's all you have).

And a star tip adds a nice decorative touch. The grooves it makes are a real dust catcher in the kitchen, though.

Hi there, hopefully this photo is zoomed in enough. We finished a DIY remodel and we solved the issue with the hood/ceiling transition with 1/4 inch wood trim. The gap between the drywall and hood was designed to be extremely tight so that 1/4 inch trim would be sufficient.

Here is a photo of the gap, before the mashed potatoes.

You'd have thought that the top metal piece (above the longer chimney) would have been designed to allow some adjustment to accommodate ceilings that weren't quite flat. The mashed potatoes still would have been needed to fill the hole near the wall though.

I would find a metal fabricator to make you a nice trim piece in stainless steel that can be scribed to the ceiling. Or pay a really really good plaster guy to float out the ceiling. I think the stainless trim will be cheaper and cleaner!

If the gap is a .50 inch or less: have this same issue. i am going to use this self sticking pvc stainless steel color finished trim to mitigate the gap. here is the Home Depot link, but I also found the exact same product on Amazon for the same price. pack of 3 - 24” pieces for $19.99:

https://www.homedepot.com/p/Aspect-Stainless-24-in-Vinyl-Backsplash-Trim-3-Pack-935-50/313854875#overlay