I've made a handful of D's and am about to make a few again soon so I'll be curious to see other peoples methods. Suppose it will depend, in part, on what tools you have available. Lots of possibilities.
For my method, I start out by putting a slight taper on the glued blanks with either a jointer (effective but potentially dangerous without a good jig) or a bandsaw. If aiming to have even thickness for the whole handle, this is obviously not needed.
Next I'll mark out on each end the shape of the D and placement of the ridge. These become guidelines to rough out the shape. If i were making many, smart move would probably to make one handle out of scrap wood and cut it into segments so I could use them as templates....but for a hobbyist like me, that level of repeatability is overkill.
For shaping, I like to treat it more like something you'd throw on a lathe. In other words, get it close to the final shape before I jump in to the actual detail work. To Stefan's post, this helps save my fingers a little bit later. For this rough out, I knock off edges and extra material with the bandsaw by tilting the table to angles before cutting. I'm essentially making it like an octagon. With handtools, the same can be done pretty easily with a sharp block plane or spoke shave if you have a good vice to hold the blank in. (I wouldn't use a chisel. I've done plenty of chisel carving, but doing it carefully isn't very efficient. It takes a while and is easy to mess up)
Once I am reasonably close to the final shape, then I hit the belt sander.
For shaping, autobody files are also a great trick if you want slower cutting and more control. Some woodworkers use these with fine inlay projects and get great results. They're super sharp but leave a smooth clean cut. Think the technical name is a smooth finish milled tooth hand file. Often they are flexible, or you can get curved ones. At about $25 to $40 they're worth having in the toolbox for any woodworking doing carving/shaping.
Hope that helps.