Boil spaghetti in well-salted water until 1 minute shy of al dente. Reserve 1/2 cup pasta water before draining.
Brown Butter the Shrimp
In a wide skillet over medium-high heat, melt butter and let it cook until amber and nutty smelling.
Pat shrimp dry, season with salt and pepper. Add shrimp in a single layer and sear 60–90 seconds per side until pink and caramelized. Remove and set aside.
Build the Sauce
In the same pan over medium heat, add remaining butter. Add garlic and cook slowly until golden and fragrant, 1–2 minutes. Add chili crisp, soy sauce, and sugar. Stir 30 seconds.
Finish the Pasta
Add spaghetti and pasta water to the pan. Toss vigorously until the sauce emulsifies and coats every strand, 1–2 minutes.
Plate and Finish
Twirl spaghetti into a high mound. Finish with scallions, a heavy chili crisp drizzle, and a lemon wedge on the side.