In a large pot, bring salted water to a rolling boil over high heat. Add the spaghetti and cook according to package instructions, typically about 8-10 minutes, until al dente. Reserve 1 cup of pasta water before draining the spaghetti in a colander.

While the pasta cooks, heat 1 tablespoon of unsalted butter and 1 tablespoon of olive oil in a large skillet over medium heat. Add the asparagus pieces, sautéing for 3-4 minutes until they're bright green and just tender.

To the skillet, add the minced garlic and optional red pepper flakes. Cook for about 1 minute, stirring continuously until fragrant. Then, add the peeled and deveined large shrimp to the skillet. Sauté for 2-3 minutes until the shrimp are pink and opaque.

Once the shrimp are cooked through, add the drained spaghetti directly into the skillet. Pour in the remaining tablespoon of butter, the tablespoon of olive oil, lemon zest, and lemon juice. Toss until everything is well coated.

Season your dish with fine sea salt and ground black pepper to taste. Serve immediately, topped with freshly chopped parsley and generous amounts of grated Parmesan cheese.