Sauce: Heat butter in a pot and braise lightly shallots. Add wine and simmer some minutes. Stir in the cold butter until sauce is creamy. Add balsamic and season to taste with salt and pepper.
Puree: Cook potatoes, peel them and cut them into cubes. Peel and dice celery. Cover celery cubes with milk and water (1:3), spice with salt and nutmeg. Add potatoes, bring to the boil and cook all for about 20 minutes. Add chopped basil, parmesan and olive oil to the vegetable. Maybe add some cream.
Sirlon: Cut slightly into skin edges every 1.5 cm and spice with salt and pepper. Fry sirloin both sides in olive oil about 5 - 10 minutes.