Heat the butter in a pan, once it gets melt to add chopped garlic and saute it for few seconds or till the raw smell goes away.
Now add all purpose flour and roast it for few seconds on low flame, do not make it brown just roast it slightly as we do while making the white sauce.
Once roasted add finely chopped onions and cook it for a minute.
Now add chopped spinach, boiled sweet corn kernels and mix it well and cook it for 2 minutes.
Once cooked add salt, mix it well.
Lastly add1/4 cup milk and mix it well and cook it for few seconds.
Once cooked it will get slightly thick as I have added maida.
Once gets slightly thick add rest 1/4 cup of milk or you can add more or less milk as per your required consistency.
Cook till it boils.
Now add seasoning red chilly flakes, black pepper, Italian seasoning, mix it well
Add 2-3 tbsp of grated cheese, mix it well.
Once the mixture becomes medium thick switch off the flame as the mixture will become thicker when cool down. Transfer the mixture to another pan and keep aside to cool down for some time.
Do not make thin mixture otherwise sandwich will become soggy.
To make Sandwich:
Take one bread slice and spread the thick layer of the spinach corn mixture evenly
Grate some cheese on top if you want to make it cheesier and cover the mixture with another bread slice.
Apply butter on both the sides and cook it on medium low flame by pressing it with the spatula from both the sides till it becomes golden brown and crisp.
Cheese Corn Spinach Sandwich is ready to serve.
Video
Notes
You can adjust the quantity of corn and spinach as per your taste. Add more cheese as per your liking.