4 (4-ounce) tuna steaks (tuna loin)
1 cup sesame seeds
15 minutes before cooking the tuna, pull it from the refrigerator and let it come up to room temperature. This promotes proper doneness. By tempering the tuna portions, you ensure that the center of the loin is slightly warm – but still rare – by the time the outside is seared.
Preheat oven to 275°F. Line a baking sheet with parchment paper and spread the sesame seeds out on the sheet evenly. Toast the sesame seeds in the oven for 10 to 15 minutes or until they are light golden brown and fragrant. The oil in sesame seeds burns at a low temperature, so it is important to watch the seeds closely while they are in the oven.
When the seeds are a light golden brown, remove them from the oven and let cool. Set aside ½ cup of the sesame seeds for the tahini if you are making it.
Set a sauté pan or cast iron pan over medium heat.
Place the tuna on a rack over a baking sheet. Pat it dry with paper towels and season on all sides with salt and pepper.
Add enough grapeseed oil to the pan to form a thin layer. When the oil starts to shimmer, place tuna in the pan gently. Sear the tuna on that side for 30 seconds without moving.
When the tuna releases easily from the pan and the bottom is golden brown, use a fish spatula to flip tuna and sear on the second side for 30 seconds without moving.
Test the tuna for doneness using a cake tester. It should be slightly warm in the center but still rare. If it is not done, continue cooking in the pan, rotating it every 10 seconds.
Turn off the stove. Carefully remove tuna from the pan using the spatula and delicately place on rack over a baking sheet.
Roll the seared tuna in the toasted sesame seeds.
Slice the tuna into ¼ inch slices, allowing your knife to do all the work (minimize downward pressure and use the entire length of the blade). It is important to use a very sharp knife when slicing tuna. Fish should be rare, but slightly warm. If eating tuna on its own, serve with soy sauce.