In a cast-iron enamel Dutch oven, add one tablespoon of oil to the pot along with the diced onion and carrots. Sauté on low heat until the onions are translucent. Add the crushed garlic cloves and stir for one minute until fragrant. Transfer to a prep dish and set aside.

Preheat the oven to 180°C/356°F.

Cook the pasta according to package instructions, drain, and set aside.

To make the bechamel sauce (creamy white sauce). In the Dutch oven, melt the butter on low heat. Add the flour to the melted butter and stir to combine into a paste. Cook, stirring continuously, on low heat for 5 minutes.  This is needed to cook out the flour.

Add 1 cup of milk, continually stirring to allow the milk to incorporate into the flour mixture (or roux). At this stage, change from using your wooden spoon to a whisk. It will make it much easier to get a smooth, creamy sauce. Gradually add the remaining milk a little at a time, stirring continuously until the mixture resembles a thick, creamy sauce. A bechamel sauce can take a lot of liquid, so don’t be afraid if it looks really runny. Cooking the sauce will cause the sauce will thicken. If it thickens too much, just add more liquid.

Strain the tuna, keeping the liquid. Using the tuna liquid, continue to cook the sauce, adding it in the same way as the milk. The sauce should coat the back of a spoon but not be too thick. It will continue cooking/thickening while in the oven, so I like to start with a thin sauce.

Strain the corn kernels, keeping 2 tbsp of the liquid for the mornay sauce.

Add the cheese and stir through to let it melt in.

Add the onion, garlic, and carrot mixture as well as the drained tuna, frozen peas, corn, reserved corn juice, and cooked, drained pasta. Stir and combine thoroughly. Either continue to bake the tuna bake in your Dutch oven or transfer the mixture to a large oven-proof baking dish.