First I thrown the base piece. Note the thick rim. It gives me a nice wide area on which to attach the top section, and will also be a design element in the finished piece. I let this piece set up to soft-leather- hard before attaching the top. This particular base piece was made with about 12 pounds of Standard 553 Buff clay. It's a little groggier than what I normally like to use, but it throws very nicely.
Next I throw the top section, leaving it about 3/4 of and inch thick. It will be pulled and thinned after I attach it to the base. I usually make this in a cone shape, because it's easier than opening it really wide, and it's more stable once I attach it to the base. There is no bottom to this section. It's just a ring.
After scraping all the slurry off of the top ring and scoring the rims of both sections, I flip the top ring over and place it on the bottom section. Then I cut off the bat and work the two pieces together, making sure they are well joined.
I like to clean up and refine the lip before I start pulling the top section. It's easier to deal with it while the wall is still thick and stable. Then I pull the top section to thin it out, and shape it to achieve the final form.
To make 35-45 pound pieces, I will throw the base section with two 12-13 pounds pieces, joined seamlessly, then add another section using this method once it has set up a bit. In theory, I could keep adding sections. The problem is that they don't always stay perfectly centered as I work upward, and it would be very difficult to control if there was too much wobble.
This method also works very well with smaller pieces. My students often do stacked forms with 5-8 pound sections, because that's all they can center. It allows them to make much larger pieces than they could in one piece. Give it a try!