Thin asparagus spears are preferable, as they are less fibrous. If you use thick stalks, you’ll need to peel them before steaming. If you have a steamer basket (or stainless steel colander) that fits over your pasta pot, use it instead of an asparagus steamer. This dish tastes equally well hot, at room temperature, and cold, especially as a midnight snack. We like ours tossed with capellini.
1 large handful (25-30) thin asparagus spears 2-3 red torpedo onions or 1/4 red globe onion 2 teaspoons olive oil 2-3 tablespoons nutritional yeast, to taste 1-2 teaspoons lemon zest, to taste large pinch of coarse salt pasta water to thin, if needed
Snap off the woody ends from your asparagus stalks. Thinly slice your onions; there should be enough to loosely pile into a 1/3 measuring cup. If using a red globe onion, cut a few thin-as-possible half moon slices, then cut into small strips about 1/4 inch long. Set up your steamer, your pasta pot (if not using to steam the asparagus), and a small cast iron or nonstick skillet for the onions.
Steam asparagus until fork tender. While the asparagus is steaming, put a teaspoon or two of olive oil into a small skillet over med heat. Sauté the onion until it begins to caramelize, then remove from heat and transfer to your food processor. When the onion and asparagus have both finished cooking, begin heating your liberally salted pasta water.
Cut the asparagus into 1-inch pieces and add to the food processor. Pulse a few times until the mixture is almost puréed. Transfer to a small bowl and stir in the remaining ingredients. If you need additional liquid, add some of the pasta water, a tablespoon at a time. Season to taste with salt and additional lemon zest, if needed.
Drain your pasta, reserving a couple of tablespoons of the cooking water. Add the pesto and gently toss to coat, using some of the reserved water if it’s too thick. Season with cracked pepper and coarse salt at the table.