In a saucepan, melt Butter (2 tablespoon) Add All-Purpose Flour (3 tablespoon) and stir to combine over a low heat. Add Milk (3 cup) and stir until mixture thickens, about 5 minutes.
Add Egg (1) and beat it through before it starts to cook. Season with Salt and Pepper (to taste).
Add Canned Tuna Packed in Water (12 ounce) and Canned Diced Tomatoes (14.5 ounce). Stir to combine, breaking up larger chunks as you go.
Bring a pot of water to boil and cook Fettuccine (500 gram) according to package directions.
Pour sauce over the noodles. Serve immediately and enjoy!