Slice the beef thinly and pound to flatten. Set aside in the refrigerator. Saute the white and portobello mushrooms together with yellow onion in cooking oil. Add the potatoes and 1 teaspoon olive oil and continue to cook until browned and tender. Season with salt and pepper and cool slightly.
Take the beef and place some potato mixture onto the center of each slice. Roll to make roulade. Bake the rolls in the preheated oven for about 2 minutes.
Take half of the dried shiitake mushrooms and place in blender or food processor. Blend into fine powder. Mix powder with tea and set aside.
Bring water to a boil. Add shallot, lemon grass, ginger, Bonito flakes, soy, remaining dried mushrooms and kelp. Let simmer for 5 minutes. Add in 1/2 of tea mixture. Let steep for 5 minutes and strain.
Place remaining tea mixture into a tea ball or filter. Immediately before serving pour sherry into liquid and liquid into teapot fitted with filter.
Place 1 to 2 drops truffle oil into each serving cup. Pour tea from pot into cup and serve on side of Kobe beef.