In a small saucepan, bring 2-½ cups of water to a boil.
Add the noodles and cook for 2 minutes.
Add the flavor packet; stir and continue to cook for another 30 seconds.
Remove the pan from the heat and carefully add the egg.
Do not stir; pull the noodles over the egg and let sit for one minute to poach.
Carefully transfer everything to a serving bowl; add the butter, cheese and sesame seeds; mix well.
Garnish with the scallions, if desired.