In a spice grinder or with a mortar & pestle, grind 2 Tbsp black peppercorns, 1 tsp white peppercorns (optional), 2 Tbsp sesame seeds, 1/2 tsp salt together until it becomes a relatively fine powder. Spread mixture on a plate. One at a time, press tuna steaks into the spice mixture, coating both sides. Set tuna steaks aside. In a saucepan (NOT over heat!), whisk together 1 Tbsp wasabi powder, 2 Tbsp water until smooth, allow to sit for 5 min (If you don’t have wasabi powder, use ~ 2 Tbsp prepared wasabi, omitting the water). When 5 min have passed, whisk in 2 tsp rice vinegar, 1/2 tsp soy sauce, and 1 cup heavy cream. Turn burner heat on to medium, heat sauce just to a simmer. Allow to simmer gently for 5 minu, as you prepare the tuna steaks. Heat 2 Tbsp olive oil in a nonstick fry pan or skillet. Gently transfer tuna steaks to the pan, leaving at least 1″ space between each. Cook for a minute and a half on the first side, then flip and cook a minute and a half on the second side. This will give you a nice rare tuna steak – cook for longer if you prefer it to be more cooked. Slice tuna steaks, fan them out, and serve with wasabi cream sauce. Enjoy!