The longer you cook the hash and butter together, the sooner the effects seem to come on. Don't let the butter bubble too much, or you can taste the hash in the end-product.
Vary the sugar according to the "bitterness" off the hash. I can't really explain that, but if you eat raw hash too, you'll know what I mean.
Vary the flour to get chewy/fluffy brownies.
about 1dl of buttermilk is pretty good too added just before the sugar, add extra five minutes before adding the eggs.
when you put the dark shokolade in, this is the time to add other things like chopped walnuts, M&M's, pecans, and so on. I like this white shokolade with prailenes added (also looks cool with white swirls in the end product). I'm going to try caramel one of these days too.
Hash oil will work too, although it if you can smell any alcohol in the oil, you should heat the alcohol out before mixing into the butter.