For this boomerang, I start with a block of yew that once was a turning blank. If I recall correctly, I bought it at Cropp Timber in Hamburg.

Note that the wood is oriented such that the growth rings are as vertical as possible. This is the most dimensionally stable orientation for the wings.

First, I plane one face to make it perfectly flat. As long as the block of wood is thick enough, I don't bother with the planing board; I just clamp it using the Wonder Pup and some 3/4" holes. I check for flatness using a ruler, but also try the piece on a flat surface to see if it's rocking. In that case, I plane some more diagonally.

I mark the freshly planed reference face so that I know where I work from.

While I aim for a final thickness of about 6 mm (1/4"), I need some room for inaccuracies during sawing, so I set the marking gauge to 8 mm (5/16").

Using the marking gauge, I scribe a line 8 mm from the flat face. The little notch in the corner is used to start the saw.

Now this is the tricky part. I saw down the scribed line, taking care to stay on the waste side. When the cut gets deep enough, I use a small wedge in the kerf so the saw won't bind.

Rats. I have managed to saw into my workpiece. At this point, I have decided to start over from the other side, although those two sawcuts will never be truly parallel. I will clean that up later; this is the reason why I started with 8 mm, giving me some wiggle room.

After ripping the piece for the first wing, I plane the other side of it flat on the planing aid.

It is important to also get rest of the wood perfectly flat again so I have a good reference for ripping the second wing. Note that I now use the planing board for the large piece as well as my block of wood is not high enough for planing over the Wonder Pup anymore. 

These are the two boards that will become the two wings. Note the continuous grain pattern across the two edges.

I unfold the two pieces like a book (note the cute "book" drawing on the boards), yielding a nicely symmetric figure. This is how I will arrange the two pieces in the final boomerang. The hatched area on the top right is my little sawing blooper from above.