Put the flour into a small heatproof bowl. Gradually add the milk 1 tablespoon at a time stirring well each time. (If you add it all at once, it will make lumps.)
Microwave at 600 W for 30 seconds. Stir well with a spoon. Microwave again for 15 seconds and stir. Microwave for another 15 seconds and mix again.
Once the mixture is thickened, add the butter, salt and pepper and mix. Add the chopped shrimp and corn.
Divide the mixture into 2 muffin cups, sprinkle 1 teaspoon each cheese and bake in the toaster oven until the cheese melts. Enjoy.
Story Behind this Recipe
You see the frozen mini gratin at a store. I thought that it would be budget-friendly and healthier it was prepared at home. I came up with a recipe that is quick enough to make it on a busy morning.
You can make a mini gratin for a bento box in 10 minutes using white sauce made in a microwave. It can be stored in the freezer also. If you're going to use it straight from the freezer, microwave it for about 30 seconds. You can add anything that you have at home, such as ham, bacon or cooked vegetables like broccoli.