In a bowl big enough to fit all mushrooms, mix 2 tbsp olive oil, a tbsp of balsamic vinegar and plenty of salt and fresh ground pepper. Whisk until you have an emulsion. Add mushrooms and toss to coat well. Leave these in the fridge until you are ready to cook them, but at least for half an hour.
In the meantime, make the stuffing. Start with 50 grams of paneer (or ricotta if that's what you have). Mash well. Add 2 tbsp grated parmesan cheese and 8-10 basil leaves that you have chopped finely. I find that cutting the herbs with scissors is usually much quicker and neater than using any knives. Also add salt to taste but go easy here because there's salt already in mushrooms and in parmesan.
When you are ready to eat the mushrooms, preheat the oven to as high as it will go. Mine goes up to 270C. Fill each mushroom with the stuffing and arrange on a baking tray. Bake on the top rack of the oven until the mushrooms are cooked through and the stuffing gets a little browned on top.