Step 1

Cook pasta according to packet instructions. Drain and set aside.

Step 2

Preheat oven to 200C. Grease a large casserole dish.

Step 3

Heat oil and butter in a large saucepan. Add onion and cook over medium heat for 4 minutes until soft. Stir though flour and allow to cook for 1 minute. Gradually add milk, whisking to create a smooth sauce. Simmer for 2 - 3 minutes to thicken slightly. Season well with salt and pepper, then stir through cheese. Add tuna and cooked pasta, and stir to combine.

Step 4

Pour pasta mix into prepared casserole dish. Top with potato gems and sprinkle over a little extra cheese.

Step 5

Bake for 20 minutes or until potato gems are golden and crispy.