How to Make It
On a work surface, cut the corn kernels off of the cobs; using the sharp side of the knife, scrape the pulp off the cobs. You should have 4 cups of kernels and pulp. Transfer the kernels and pulp to a blender and puree until smooth. Strain the puree through a fine sieve, pressing on the solids.
In a large saucepan of salted boiling water, cook the spaghetti until al dente. Reserve 2 cups of the cooking water, then drain the pasta.
Wipe out the saucepan and melt the butter in it. Add the guanciale and cook over moderate heat, stirring occasionally, until the fat is rendered, about 7 minutes. Add the shallots and garlic and cook, stirring, until softened, about 3 minutes. Add the spaghetti, strained corn puree, 1 1/4 cups of the pasta cooking water and the lemon juice. Cook over moderate heat, tossing, until the sauce is thickened and creamy, 3 to 5 minutes; add more of the cooking water if necessary. Season the pasta with salt and pepper and very gently fold in the crab. Transfer to shallow bowls and drizzle with olive oil. Garnish with lemon zest and shichimi togarashi and serve right away.