Linguine with Asparagus, Peas & Herbs

Linguine with Asparagus, Peas & Herbs
1 lb. (500 g.) asparagus
Kosher salt for cooking vegetables and pasta
1 cup (5 oz./155 g.) fresh shelled English peas or frozen baby peas
3 Tbs. unsalted butter
3 Tbs. extra-virgin olive oil
6 green onions, including 3 inches (7.5 cm.) of green tops, thinly sliced on the diagonal
2 yellow onions, chopped
6 oz. (185 g.) baby spinach, coarsely chopped
Fine sea salt and freshly ground pepper
1/2 cup (4 fl. oz./125 ml.) heavy cream
2 Tbs. minced fresh mint
1/4 cup (1/3 oz./125 ml.) minced fresh flat-leaf parsley
1 lb. (500 g.) linguine Freshly grated Parmigiano-Reggiano cheese for serving In a large pot, bring 5 qt. (5 l.) water to a rapid boil.   While the water is heating, snap off the tough ends of the asparagus. Using a vegetable peeler, peel away the thick skin to within about 2 inches (5 cm.) of the tips. Cut the spears crosswise into 1-inch (2.5 cm.) pieces, leaving the tips intact. Add 2 tablespoons kosher salt and the asparagus to the boiling water and cook until tender, about 6 minutes. The asparagus must not be crunchy. Using a wire skimmer or slotted spoon, transfer the asparagus to a bowl. Add the peas to the boiling water and cook for 1 minute. Drain and add to the bowl holding the asparagus. Set aside. Reserve the water in the pot.   Meanwhile, in a frying pan large enough to accommodate the pasta later, melt the butter with the olive oil over medium-low heat. Add the green onions and yellow onions and saute until translucent, about 5 minutes. Stir in the spinach, 1/2 teaspoon sea salt, and several grinds of pepper and saute, tossing often, until the spinach is wilted, about 3 minutes. Add the asparagus and peas, then stir in the cream and heat until hot, about 1 minute. Add the mint and parsley and stir well. Taste and adjust the seasonings. Remove from the heat and cover to keep warm.   Return the water to a rapid boil. Add 2 tablespoons kosher salt and the pasta to the boiling water, stir well, and cook, stirring occasionally, until al dente, according to package directions.   Just before the pasta is ready, if the sauce has cooled, return it to medium-low heat to warm, then remove from the heat. Drain the pasta, add to the sauce in the pan, and toss until the strands are well coated with the sauce. Transfer to a warmed large, shallow serving bowl or individual shallow bowls and serve right away. Pass the cheese at the table. Serves 4-6.