Slice bok choy in half lengthwise and then diagonally.

Rinse peeled shrimp and pat dry with paper towels.

Boil water in a pot, add salt, and cook spaghetti 1 minute less than package instructions. Drain.

Heat butter in a pan over medium heat, add bok choy, and sauté until softened. Add shrimp and cook until color changes.

Add flour to the pan and stir until no longer powdery. Gradually add milk, stirring until thickened.

Season with salt and pepper, add spaghetti, and toss to combine.