Lots of ways to go about it, all of which produce a slightly different result
Spherical radius dish is of course widely used.
For a cylindrical radius, take a piece of plywood and put two thin boards along under the edges of it so it's suspended at the height of arch you want to create. Then clamp down the middle of the two edges between the supports. Actually creates a parabolic curve.
Another method is to dish out a solera workboard using finger planes, gouges, sanding, whatever. You can do non-spherical curves this way, which is nice.
A somewhat more time consuming and less consistent method is to plane/sand an arch into your braces, and then glue them to the plate one at a time using cam clamps and a flexible (but stiffer than the top) backing slat to help distribute the pressure and spring the top onto the brace. This is the method used in Cumpiano and Natelson's book, and is what I do. It still allows some useful non-spherical curves, such as arching the upper transverse brace, but flattening the portion that lies directly beneath the fingerboard (especially important if you have a flat headblock extension butted to it).
An even less consistent (but fast) method, is to dry out the plate before bracing it with flat braces on a flat workboard, and let it create its own dome by swelling up when it returns to normal moisture.
That's all I can think of for now.
