Although a crucial step in the process, this one is so straightforward, a good look through the images will give you all the information you need!

As you can see from the image progression series above, I started on the two small branches I had on the surface of wood, once those were taken down, I started pulling from the center out (a pull cut is a little bit cleaner than a push cut, at the relatively low surface speed the center of any vessel has), first taking out the barks, and than starting to dig well into the wood. I leave the edges of my bowl to the end to prevent stresses on the side walls of the bowl as the narrow profile is being created.

What I like the most about working with uneven wood surface, like this bowl, is that for a long time into hollowing the inside of the vessel, you can see clearly with your own eyes the width of the walls in the ghost image created from looking at something spinning which is not whole, Like you being able to see the bowl gouge cutting inside the bowl in one of the pictures. Of course that later on, when the walls are already high, I will use a caliper, both to gauge the depth of the bowl, and both for the widths of the walls using a special curved caliper.

Notice how I position my tool rest in the last couple of images, to allow me to cut along the walls of the bowl with as little space as possible between the wood and the gouge. This will prevent the gouge from vibrating and creating marks on the walls of the bowl which will be problematic to sand even later.