Method

1. Preheat oven to 180°C fan-forced (200°C conventional). Lightly grease a 2.4L-capacity ovenproof dish with oil.

2. Cook pasta in a saucepan of boiling, salted water, following packet directions, until al dente. Drain pasta and return to pan, off the heat.

3. Meanwhile, melt butter in a large deep frying pan over medium heat. Add onion and cook for 4 minutes, until softened. Stir in flour and cook, stirring, for 1 minute, or until bubbles appear. Whisk in milk, 125ml at a time, until combined, then whisk in mustard and zest. Cook, stirring, for a further 2 minutes. or until sauce is very thick. Season. Remove from heat.

4. Add tuna, corn and cheese. Gently stir to combine, breaking tuna into chunks as you stir. Stir through pasta. Set aside.

5. Brush and layer filo pastry sheets with extra butter. Line greased ovenproof dish with pastry, allowing edges to overhang. Spoon pasta mixture into dish and gently roll pastry sides in to create a neat edge.

6. Sprinkle breadcrumbs and extra cheese over top. Bake for 20 minutes, or until cheese topping is golden. Garnish with herbs and serve.