1 teaspoon of dijon mustard 1/2 an onion, chopped 2 tablespoons of butter 1 tablespoon of plain flour 1 cup of milk, 1 cup of grated cheese olive oil, salt and pepper to season
Firstly open the tins and drain well. Sauté onion in a small amount of oil until transparent. To create the base sauce for this mornay, add flour to the onions and quickly add butter. Have the
heat fairly low but hot enough to melt the butter.
You must keep stirring flour and butter with a wooden spoon until it is all blended. You will notice that the flour and butter
have binded and become solid but don't worry, this is meant to happen. Keep stirring for a few minutes on low heat as you need to cook the flour to remove the floury taste that can result if not cooked long enough.
After some practice you will be able to gauge how long you need to cook it for. Now turn the heat up and add milk in small batches, about a tablespoon at a time at first and keep stirring all the while. You need to do it this way or your sauce will be
lumpy. As the sauce combines you can add more milk until it becomes creamy, lower the heat again. Add the mustard, salt, pepper and stir through. Taste the sauce to make sure it is just right.
Add tuna and corn and heat through until it simmers. Keep stirring as the sauce can thicken quickly if left on too high. Place in a heatproof casserole dish and sprinkle the cheese over the top. Melt the cheese under a hot grill if possible as this is the quickest way to brown the cheese. If not a hot oven is fine. Once cheese is browned remove from oven and serve with rice or pasta.