Place shallot, bay leaf and wine in a small saucepan and bring to a boil. Reduce until the wine is almost evaporated, about 5 minutes. Remove from the heat, discard bay leaf and transfer to a small bowl. Add sour cream, lemon juice, 1 teaspoon dill, mustard and 1/4 teaspoon salt; stir to combine.
Put breadcrumbs, pistachios, the remaining 1 teaspoon dill and 1/4 teaspoon salt in a blender or food processor. Process until finely ground. Transfer to a shallow bowl. Dredge both sides of the tuna in the pistachio mixture.
Heat oil in a large nonstick skillet over medium heat. Add the tuna and cook until browned, adjusting the heat as necessary to prevent burning, 4 to 5 minutes per side for medium-rare. Serve with the lemon-dill sauce.
Note: We like Ian¿s brand of coarse dry whole-wheat breadcrumbs, labeled ¿Panko breadcrumbs.¿ Find them in the natural-foods section of large supermarkets. Or, make your own breadcrumbs: Trim crusts from firm sandwich bread. Tear the bread into pieces and process in a food processor until coarse crumbs form. One slice makes about 1/3 cup. Spread the breadcrumbs on a baking sheet and bake at 250°F until dry and crispy, about 15 minutes.