In a spice grinder or mortar and pestle, combine freshly cracked black peppercorns, optional white peppercorns, sesame seeds, and salt. Grind until you create a fine powder.

Press each sashimi grade tuna steak into the spice mixture, ensuring all sides are well coated. Set the seasoned tuna steaks aside for about 5 minutes.

In a cold saucepan, whisk together the wasabi powder and water, then let it rest for about 5 minutes. Whisk in the rice vinegar, soy sauce, and heavy cream until well combined.

Place the saucepan over medium heat and bring the wasabi cream sauce to a gentle simmer for about 5 minutes, stirring occasionally until it thickens slightly.

In a nonstick skillet, heat olive oil over medium-high heat until shimmering. Sear the seasoned tuna steaks for 1.5 minutes on each side.

Remove the seared tuna steaks from the skillet and allow them to rest for a minute before slicing them into thin, diagonal pieces.

Drizzle the creamy wasabi sauce over the sliced pepper crusted tuna and serve. Optionally, serve over arugula or alongside grilled vegetables.