Place star anise, soy sauce, garlic, sugar and rice vinegar in a small skillet. Bring to a boil, reduce heat and simmer for a minute or until only 1/4 cup remains. Strain out star anise and reserve. If you are using five spice powder instead of star anise, add it to the liquid now. Let it cool while you boil the beef. Bring 3 quarts water to a boil. Add beef and boil for 15 to 18 minutes. (depending if you like it very rare or just rare.) Remove the beef from water and let stand at room temperature for 15 minutes while you finish mayonnaise. Mix cooled reduced star anise liquid with mustard and mayonnaise. Add sesame oil to taste, 1/2 teaspoon salt and crushed red pepper. Thin mayonnaise with just a teaspoonful of water to make it spreadable.
When the beef is cool, slice it vertically, with the grain, into 1/2-inch wide slices. Then slice the long slices, across the grain into 3-inch long by 1/2-inch wide strips. Spread some mayonnaise on a dinner plate. Center a clump of watercress in the center of your plate. Surround watercress with a wreath of beef slices and sprinkle meat with coarse salt, freshly ground black pepper and chives. Drizzle more mayonnaise on beef edges if you wish (or for a more professional look, transfer mayonnaise to squirt bottle to drizzle over beef edges)