I asked a couple of the guys I know that make bows and they started with simple arcs in the back of the riser.
They cut to the line (with a band saw), on each piece or stacked them and cut them (as DMax says above)simultaneously. then sand them, I hold mine up to the light. I do believe the secret is the thin bending contrasting accent between both pieces.
It has worked for me (and if like me you dont have all the tools you would like to have),
Good Luck
Mike