1. Mix the mayonnaise, chives, and tarragon in a small bowl. Cover and refrigerate until ready to use.

2. Cook the bacon in a large skillet over medium heat until browned and crisp, about 8 minutes. Transfer to paper towels to drain. Cut each strip in half to make 12 pieces total. Pour out and reserve the bacon fat. Wipe the skillet clean with paper towels.

3. Line a baking sheet with wax paper. Whisk the eggs in a shallow dish. Mix the flour, cornstarch, salt, and pepper in a second dish. Dip each crab in the eggs, then in the flour to coat completely. Transfer to the baking sheet and refrigerate for 15 to 30 minutes to set the crust.

4. Heat the oil and reserved bacon fat in a large skillet over medium-high heat until the oil shimmers. Carefully add the crabs to the skillet. (The crabs could splatter, so be careful.) Cook until the undersides are golden brown, about 3 minutes. Using a thin slotted metal spatula, turn the crabs and cook to brown the other sides, about 3 minutes more. Using the spatula, transfer the crabs to paper towels to drain briefly.

5. Spread the buns with the herb mayonnaise. Top each bottom bun half with a crab, 3 bacon slices, 2 tomato slices, and a lettuce leaf, then the top bun half. Cut each sandwich in half and serve immediately.