Finely chop garlic.
Wash leeks, halve lengthways and check where the leaves turn dark green — sand can sometimes get trapped there.
Slice each half into thin half-moons.
Pat meat dry, then season generously with salt and pepper from all sides.
Bring a large pot of water to boil. Salt generously.
2. Cook meat and pasta
Heat a teaspoon of vegetable oil over medium-high heat, add the tenderloin medallions, and sear for 2 minutes on each side until a crust forms, then cook for a couple more minutes, flipping from time to time.
Carefully add fusilli to boiling water, stir well, and cook over medium heat for 9 minutes for al dente, or 10 minutes if you prefer your pasta softer.
Transfer meat to a plate and let rest until step 5. Do not wash the pan.
3. Start cooking sauce
Heat another 1 tsp vegetable oil in the same frying pan. Increase heat to medium-high.
Sauté garlic for 30 seconds until fragrant, then add leeks and a pinch of salt.
Cook for 3–4 minutes, until leeks are softer and of golden colour.
4. Finish sauce
Pour chicken stock over vegetables and warm through for 30 seconds, then gently stir in cream. Bring to a boil, then reduce the heat .
Simmer over medium-low heat for 3 minutes, until sauce thickens slightly.
Season with pepper and check for salt.
5. Serve
Arrange tenderloin over pasta—you can slice meat into strips first, if you like. Spoon over sauce and finish with cheese on top.