Ingredients

Equipment Needed

• •Heavy-bottomed saucepan for the cheese sauce
• •Large ovenproof baking dish (about 2 litres)
• •Wooden spoon or whisk

Instructions

1. 1

   Cook the pasta

   Bring a large pan of well-salted water to a rolling boil. Cook the penne until it still has a bit of fight in it, a minute or two short of what the packet says. It's going into a hot oven next, and pasta that's already soft will turn to mush. Drain it, but save a mugful of the starchy cooking water. You may not need it, but it's good insurance.

   Salt the water until it tastes of the sea. This is the only chance the pasta has to absorb seasoning from the inside out. Be generous.
2. 2

   Make the cheese sauce

   Melt the butter in a heavy saucepan over a medium heat. When it foams, add the flour and stir it in with a wooden spoon. Cook for a minute or so, stirring constantly, until the paste smells biscuity and has lost its raw, floury pallor. Now add the milk, a good splash at a time, stirring well between each addition. The first few splashes will seize into a thick paste. That's right. Keep stirring, keep adding milk, and it will loosen into a smooth, glossy sauce. Once all the milk is in, let it simmer gently for five minutes, stirring now and then, until it coats the back of the spoon.

   If it goes lumpy, don't panic. Take it off the heat and whisk hard for thirty seconds. Most lumps surrender to persistence. If they don't, push it through a sieve and carry on. Nobody will know.
3. 3

   Season the sauce

   Take the pan off the heat. Stir in about two thirds of the grated cheddar, keeping the rest back for the top. Add the mustard. Season with salt and pepper, then taste it. The sauce should taste properly cheesy and slightly sharp from the mustard. If it tastes bland, it needs more salt. If it tastes like wallpaper paste, it needs more cheese. Trust your mouth.

4. 4

   Combine everything

   Set the oven to 200C/180C fan. Tip the drained pasta back into its cooking pan or into a large bowl. Flake the tuna over it, breaking it into rough chunks rather than shredding it fine. Add the sweetcorn. Pour over the cheese sauce and fold everything together gently until the pasta is well coated and the tuna and sweetcorn are evenly scattered through. If it looks thick and claggy, loosen it with a splash of the reserved pasta water. It should be saucy. The oven will thicken it further.

5. 5

   Bake until golden

   Pour the mixture into a baking dish, something that fits it without too much spare room. Scatter the remaining cheddar over the top. If you want a bit of crunch, add a handful of breadcrumbs over the cheese. Bake for twenty minutes, or until the top is golden and blistered in places and you can see the sauce bubbling at the edges. Let it sit for five minutes before serving. The first portion out of the dish is always the messiest. That's fine. Nobody minds.

Chef Tips

• •Make the cheese sauce yourself. I know there are jars. I know they're convenient. But a proper white sauce made with butter, flour, and milk takes ten minutes and tastes incomparably better. Once you've done it three times, you won't need the recipe. Your hands will know.
• •Mature cheddar, not mild. Mild cheddar melts obediently but tastes of nothing in particular. You want a cheese that stands up and makes itself known through the sauce. A good mature cheddar, or even a mix of cheddar and a spoonful of parmesan, gives the sauce backbone.
• •Don't shred the tuna too finely. You want to find it in the dish, in proper chunks that have some texture against the soft pasta and the smooth sauce. Flake it roughly and leave it alone.
• •Leftovers reheat well the next day with a splash of milk stirred through before going back into the oven. The pasta absorbs the sauce overnight, so it needs loosening. Second-day pasta bake, heated until the edges go crisp again, is a quietly excellent lunch.

Advance Preparation

• •The cheese sauce can be made a day ahead and refrigerated. It will thicken as it cools. Warm it gently with a splash of milk and stir until smooth before combining with the pasta.
• •The whole bake can be assembled, covered, and refrigerated for up to a day before baking. Add five minutes to the oven time if baking from cold.

Frequently Asked Questions

Nutrition Information

1 serving (about 520g)