Seared ahi tuna with fennel and radishes

My dad loves fish, and particularly barely cooked tuna. For our first of a mere two dinners in Eugene, we made one of our favorite fancy dinners. Press fennel seeds into boneless sashimi grade ahi tuna. Heat a cast-iron pan until it is very hot, and then sear just the outer half-centimeter or less of the fish, leaving the middles that wonderful tuna purple. Slice very thin a bulb of fennel and some radishes, and slice the fish into quarter-inch-thick (or less) strips. Layer the fennel, the fish, and the radishes in the kitchen, and cover with a very strongly shallot-y sherry vinaigrette. Serve with sourdough bread, sage-and-shallot butter, roasted garlic, and an Oregon pinot noir.