Bushmonster, it is very easy.
As BTs said, don't overheat the butter, just very lightly simmer it in butter for a short while, then strain the hash/marijuana out.
After that pretty much cook as normal. Brownies have always been easier for me than cakes, for some reason using cannabutter seems to make things a little drier. That's why it's good to add an egg even if its not listed as an ingredient, it'll help moisten up the cake a little.
Good luck, happy baking.
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