Put 3L of water 1.5 teaspoons of salt in a large pot, then bring the salted water to a boil. Add your udon noodles and cook for 9 minutes (or cook to packet instructions). Use a pair of tongs to remove the noodles and transfer them to a colander. Give the cooked udon noodles a quick rise and set aside.
Bring the salt boiling water in the pot down to a simmer, add the bok choy stems, simmer for 1 minute then add the leaves and cook for another 30 seconds.
Once you have simmered the stock, use a slotted spoon to remove the ginger, garlic and star anise. Then use a regular spoon to skim the stock. Finally, season the stock to taste with your soy sauce. Make sure you don't add too much and taste as you go.
Pre-heat a pan over high heat for at least 1 minute, turn the kitchen fans on and/or open the windows. When the pan is nice and hot, add your oil, then add your steak and sear for about 4 minutes on each side for medium rare (this is for a steak that is about an inch thick).