Easy as! A line of mud around your marked out circle, a wedge of mud on the long edge of each brick, and away you go.
I've drilled a couple of teck screws in to each side of the door frame. This will give it something to tie it into the mortar of the wall.
I set aside the weekend to lay the dome. During the week I made sure that the dome and door was marked up. I had my bricks split in half and piled up next to the site. I'd bought 3 bags of mortar mix (turned out I needed another one). Every thing was ready to go as soon as I dragged myself out of bed on Sat morning.