For the Polenta, cook the Polenta, water, milk, butter, salt, and pepper together. Keep on low heat and stir continuously for about 5 minutes.
Keep your attention towards the Polenta, cause it can burn on really quickly and cooks up super fast. Remove it from the heat once it starts to boil up.
Spread half amount of the polenta into a baking dish to create the first layer.
For the white sauce, heat up a saucepan with the butter.
Continue adding in the White flour. Keep on stirring with a whisk on slow heat.
Then pour in the milk. Stir well, season and keep on whisking the sauce till it gets thick by itself. Remove from the heat and keep aside.
Preheat your oven to 350 Celsius/ 180 Fahrenheit.
Mix the Tomato Sauce with the olives, basil, salt, and black pepper
Spread the mixed tomato sauce over the polenta layer
Then add the remaining polenta to form the layer over the tomato paste.
Then spread the white sauce over the polenta to create a creamy layer.
At last spread the Parmesan Cheese over the white sauce.
Bake the casserole dish for about 15 minutes at 350 Fahrenheit/180 Celsius.
Notes
Use a homemade or readymade tomato sauce. I made my own chunky tomato sauce by adding whole onions to it for texture. You can add regular ragu as well.