How to Make It
Pat scallops dry with paper towels. Set aside. Bring 2 cups fennel, potato, and 1 cup water to a boil in a small saucepan. Reduce heat to low; simmer, partially covered, until potato is tender, about 15 minutes. Drain, pressing to remove excess liquid.
Transfer fennel mixture to a food processor. Add butter, 1/2 teaspoon lemon juice, and 3/8 teaspoon salt. Process until smooth. Cover to keep warm.
Gently break apart segments of 2 tangerines; set aside. Squeeze juice from remaining tangerine into a medium bowl. Whisk in shallot, olive oil, olives, tarragon, coriander, garlic, and remaining 1/2 teaspoon lemon juice. Add tangerine segments and remaining 1 cup fennel slices; toss to coat.
Heat 1 1/2 tablespoons canola oil in a large cast-iron skillet over high until shimmering. Add 6 scallops; press gently with a spatula. Cook until sides are lightly browned, about 3 minutes. Turn scallops; cook 30 seconds or to desired degree of doneness. Transfer cooked scallops to a plate; wipe skillet clean. Repeat with remaining canola oil and remaining scallops. Sprinkle scallops with remaining 1/8 teaspoon salt. Serve with puree and salad.