Bring a large pot of salted water to a rolling boil, then add the pasta. Cook until just al dente, about 8 minutes, and then reserve a cup of pasta water before draining in a colander. Set aside.
While the pasta cooks, trim the woody ends off the asparagus, then cut into 2-inch pieces. Blanch in boiling water for 2 minutes until vibrant green and tender-crisp. Drain and set aside.
In a large sauté pan, melt the butter over medium heat until it starts to foam and smells slightly nutty, about 2 minutes.
Add the minced garlic to the pan, cooking until fragrant and golden, about 30 seconds. Be careful not to burn it.
Toss in the blanched asparagus, sauté for 2–3 minutes until slightly charred and tender but still crisp, releasing a fresh aroma.
Add the cooked pasta to the pan, then squeeze in the juice of half the lemon and sprinkle over the lemon zest. Pour in a splash of the reserved pasta water and toss everything together, coating the noodles evenly with the lemon butter sauce.
Drizzle in the olive oil, season with salt, pepper, and chili flakes if using. Toss again until glossy and well combined, about 1 minute.
Remove from heat, then give the pasta a final squeeze of lemon for brightness. Taste and adjust seasoning as needed.
Serve immediately, garnished with extra lemon zest or herbs if desired, for a vibrant, buttery, and crisp-textured dish.
