First, make the white sauce. Thinly slice the onions and heat in a microwave until softened. Heat the oil and butter in a frying pan and lightly sauté the onions.
Turn off the heat and mix the flour into the onions. Sauté some more until no longer powdery. Add the milk and soup stock granules, mix, and simmer for 5-10 minutes.
When thickened, turn off the heat and add the macaroni salad. You want just enough white sauce to coat the macaroni salad, so adjust accordingly.
Transfer to dishes and sprinkle with panko and grated cheese. Bake until browned. We use the microwave's gratin course for 20 minutes (Prepare using whatever method you usually prepare gratin.)
Story Behind this Recipe
I made a lot of macaroni salad, so I had a lot leftover.The mayonnaise had hardened slightly, so this dish rescued the sad leftovers.
It's really just like making a regular casserole dish au gratin. My salad had tuna and broccoli in it. It also had vinegar, but you can't tell after it's been baked. You can also try adding some boiled asparagus. This time, I used a 15 cm gratin dish, a 10 cm ramekin, and a 7 cm cup.