Pat steak dry and season lightly with salt and pepper. Spread 1 teaspoon sesame seeds evenly on one side of steak.
In a large heavy skillet heat oil over moderately high heat until it begins to smoke and add steak, sesame-seed-side down. Spread remaining teaspoon sesame seeds on top of steak. Cook steak 1 1/2 minutes on each side for medium-rare meat and transfer with a slotted spatula to a small platter. Keep steak warm.
Pour off almost all fat from skillet and add garlic and red pepper flakes. Cook garlic mixture over moderate heat, stirring, 10 seconds and add Sherry. Boil mixture until almost all liquid is evaporated and remove skillet from heat. Add soy sauce, vinegar, and honey and bring to a simmer, stirring. Add butter and stir over low heat until incorporated. Spoon glaze over steak.