Preparation

• Make grapefruit sorbet:
  Combine all ingredients in an ice cream maker and process until firm.
  
  Make grapefruit vinaigrette:
  Crush grapefruit segments, then add other ingredients, including salt and pepper to taste.
  
  For the tartare:
  Chop the tuna coarsely, then, in a chilled metal bowl, combine it with the oil and salt.
  To Assemble:
  Pour the grapefruit vinaigrette over the tuna, toss lightly, and mold the mixture onto the center of a plate.
  At Mantra, we garnish the plate with cucumbers in yogurt and marinated radishes, but feel free to add any cold salad fixings.Top with a melon ball-sized scoop of sorbet.
  For an upscale touch, put a teaspoon of osetra caviar on top to finish.