2Meanwhile, make the dressing: Combine the miso paste, ginger, soy sauce, and lime juice in a blender and blend, at medium speed until smooth. Add the egg and blend until combined. With the motor running, slowly add the oil. Once the dressing is smooth, add pepper to taste; you won't need salt, because the miso and soy sauce are salty. (The dressing can be made up to 1 day ahead and refrigerated, covered.)
3Add the soba noodles to the boiling water and cook, stirring often, until al dente. Drain the noodles and rinse well under cold running water. Drain well, transfer to a baking sheet, then spread out and let cool.