Heat 1 tablespoon clarified butter in small frying pan over medium-low heat. Add sliced onion and brown. Place green pepper and mushrooms on top of onion slices. Season generously with salt and white pepper. Continue cooking very slowly.
Heat 1/8 cup clarified butter in a large frying pan on high heat. Add pieces of beef and toss in butter. Season with salt and black pepper. Cook for 5 minutes, then remove meat pieces from sauce and place on a plate. Deglaze pan with diced onion, chili and port on high heat for a couple minutes. Add pimento and continue to cook liquid down. Stir in tomatoes. Add beef to sauce and stir to coat well. Remove beef to serving platter.
Scoop out avocado flesh in balls. Pour lime juice over avocado to prevent discoloration. Add to vegetables in small frying pan; season with white pepper. Combine all this well with reserved meat.
Whisk butter into sauce and pour over meat and vegetables to serve.