01 -
Heat oven to 200°C / 390°F and set out a 20 × 25 cm baking dish. Bring a large pan of water to a boil. Cook penne for 2 minutes less than the package timing, then drain.
02 -
Melt butter in a saucepan over medium heat. Stir in flour and cook, stirring, for 1 minute without browning.
03 -
Gradually whisk in milk to make a smooth sauce. Bring to a gentle simmer and cook for 3–4 minutes, stirring, until it coats the back of a spoon.
04 -
Remove from the heat and stir in mustard, salt, pepper and 60 g cheddar. Fold in drained tuna in large flakes and the sweetcorn.
05 -
Combine the sauce with the drained pasta and transfer to the baking dish. Scatter over remaining 40 g cheddar.
06 -
Bake for 18–22 minutes until bubbling at the edges and golden in patches on top. Rest 5 minutes before dividing into four portions. The sauce should stay creamy around the pasta.
07 -
Refrigerate leftovers within two hours for up to three days. Reheat with a splash of milk or water until steaming hot throughout.