The tenchirashi soba ($17.80++) from Shimbashi Soba is my dad's and my favourite.

It is served with copious amounts of crispy tempura (prawns, mushrooms, vegetables). It's amazing how the tempura stays crisp over the bed of chilled soba and broth. What I love to do is order an upsized portion of soba (+$5), mix wasabi and the onsen egg together with the soba, broth and tempura. You get an utterly delicious meal after!