What is the easiest and best way to cover a cake with sprinkles?

I recently covered a cake in sugar sparkles.  I used a buttercream frosting and let it set up in the refrigerator.  I took the cake out and started gently "patting" the sugar sparkles all over the cake.  You could put a wire rack under the cake to collect the sprinkles and reuse them.

I've done with with piping gel brushed on the cake to make it sticky and them patted them on, unless you use it on freshly applied buttercream.