Remove the stem from the tomato and dice into 2cm cubes. Slice the onion thinly.

Wash the peeled shrimp under water and pat dry with paper towels.

Boil a pot of water, add salt (not listed in ingredients), and cook spaghetti 1 minute less than package instructions. Drain.

Heat butter in a frying pan over medium heat, add onion, and sauté until softened. Add shrimp and tomato, mashing the tomato as you cook.

Add flour and stir until no lumps remain. Add milk and seasonings, stirring until thickened over low heat. Add spaghetti and toss to coat.