Rub the meat with salt & pepper and let the meat come to room temperature for 30-40 minutes. |
Slice onion thinly and set aside. |
Heat olive oil in a large pan or skillet over medium-high heat until very hot but not smoking. |
Add the 1 tablespoon butter in a pan and add meat and sear on all sides; 3-4 minutes per side. |
When meat is nicely browned, add Takara Mirin and sliced onion. |
Place the lid and cook in medium heat, frequently turning. |
Cook roast until an instant-read thermometer registers 125ºF for rare, 130ºF for medium. |
When desired temperature is reached, take out the meat from the pan and rest it for 15-20 minutes. |
In the pan which meat was cooked, add soy sauce, sake, mustard and the rest of the butter. Reduce the sauce to preferred thickness at medium to medium high heat. |
Pour sauce over the sliced meat for serving. |