That recipe is somewhat lacking in detail, and not one I would necessarily have much confidence in working well , however, I see no reason for you to try it, only use half of the other ingredients to keep the intended strength the same for each brownie (pro rata).

I'm a little dubious that the proposed method of throwing all the ingredients into a double broiler for a 'short'? (unstated) period of time would successfully extract anything like the full strength of THC from your bud.

Instead I would recommend grinding your bud into as fine a grain as you can manage and then mixing it JUST with the butter alone for as long a period as your prepared to wait in order to give the THC the best chance of binding to the fat molecules in the butter. Ideally simmering at around boiling point for about an hour (preferably a lot longer). If you can put a lid over the pan even better (prevents any THC being lost due to evaporation/vaporisation).

Once you've done that, then add the rest of the ingredients and follow the instructions as directed in the recipe.

Good luck and enjoy.

I'm cooking myself this afternoon, my legendary 'chilli con canna', by special request of some friends who are coming over tomorrow. It's gonna get messy!