How to Make It
Bring a large pot of water to a boil. Prepare an ice bath.
Prepare the Topping: Add baking soda and 1 teaspoon of the salt to boiling water. Add herbs, and cook until very soft, 3 to 5 minutes. (A parsley leaf rubbed between 2 fingers should disintegrate.) Using a slotted spoon, remove herbs, and immediately plunge into ice bath; let stand until cold.
Remove herbs from ice bath, and let excess water drip off. Place in a blender or food processor, and process until very smooth. Pour through a wire-mesh strainer into a bowl to strain off excess liquid. Discard liquid.
Stir together blended herbs, sour cream, pepper, and remaining 1/4 teaspoon salt in a bowl until combined. Drizzle with olive oil, and sprinkle with fleur de sel.
Prepare the Latkes: Rinse grated potatoes in a colander with hot water. (Hot water will act as a blanch to prevent discoloration.) Drain and squeeze the potatoes to remove as much excess liquid as possible.
Place potatoes, onion, and eggs in a bowl, and stir to combine. Stir together flour and salt in a small bowl until combined; gradually add to potato mixture, stirring until combined.
Heat Clarified Butter in a large skillet or on an electric griddle over medium-high. Drop 6 to 8 loosely packed 1/4 cupfuls of potato mixture into hot butter; press lightly with a spatula to flatten into 3-inch rounds.
Reduce temperature to medium, and cook until golden, 3 to 4 minutes per side. Place on a plate lined with paper towels and sprinkle with pepper. Serve Potato Latkes topped with smoked salmon, herbed sour cream, and tarragon sprigs, if desired.