Peel the bottom third of the asparagus stalks with a vegetable peeler. Snap each stalk where it breaks naturally; reserve 4 of the peeled bottoms for crostini (below). Thinly slice 6 asparagus bottoms and place the rest of the bottoms in a saucepan with 8 cups water and the thyme to make asparagus broth; bring to a simmer.
Heat 2 tablespoons butter in a saucepan over medium heat. Add the shallot and cook, stirring, until translucent, about 2 minutes. Add the rice and cook, stirring, until glossy, about 1 minute. Add 1 1/4 teaspoons salt. Pour in the wine and stir until absorbed. Stir in 1/2 cup of the asparagus broth until absorbed (use a ladle to add the broth, keeping the solids in the pan). Continue to add broth in 1/2-cup increments, stirring constantly and allowing the liquid to be absorbed before adding more, about 10 minutes. (You should have about half the broth left.) Stir in the sliced asparagus bottoms and the lemon zest. Add the remaining broth, 1/2 cup at a time, until the rice is just tender, 5 to 8 more minutes.
Meanwhile, place the asparagus tips in a large skillet, cover with water and season with salt and pepper. Simmer over medium-high heat until just tender, about 5 minutes.
Add the remaining 2 tablespoons butter, the parmesan and lemon juice to the risotto. Stir in the lettuce, remove from the heat and season with salt. Divide among bowls, top with the robiola and season with pepper. Drizzle the asparagus tips with olive oil and spoon over the risotto.