For Creamy Mushrooms: Heat the oil. Temper it with celery and thyme; add garlic and green chilly paste. Stir it for a minute on a medium flame. Add the mushrooms; cook it on medium flame till all its juices dry up.
To it add all-purpose flour and roast it for 2 mins on medium heat, add hot milk, stir well to avoid any lumps. Now add the cream and cook till the sauce thickens.
Creamy mushrooms are ready to be used.
You can use it just like this or sprinkle the grated cheese over it and bake at 180 degree C for 15 mins or untill the cheese turns golden. If baking, then adjust the consistency of the sauce by increasing the quantity of milk and cream.
For the sandwich: Gingerly scoop out the centre of a burger bun to avoid cutting or piercing the base.
Spread the garlic butter inside the bun and top with the filling.
Sprinkle cheese and bake at 200 degrees Celsius for 10 minutes on the middle rack.