Step 1: 1. Chop and fry the onion in a saucepan.
Step 2: 2. Drain and add the tuna and sweet corn and cook until soft
Step 3: 3. In a separate pan, make the white sauce using the all in one method, whisking all the time until thick and creamy
Step 4: 4. Remove from the heat and add half the cheese.
Step 5: 5. Boil the pasta in salted water until soft; drain
Step 6: 6. Add the pasta and cheese sauce to the tuna and mix well.
Step 7: 7. Pour mixture into ovenproof dish and sprinkle remaining cheese on top.
Step 8: 8. Back in a pre-heated oven at 200oc/gas 5 for 20 mins or until golden