Fit food processor with shredding blade, then shred potatoes and onions. Transfer to a colander lined with cheese cloth or a clean kitchen towel. Season potato mixture with 1 teaspoon salt and set aside while preparing salmon and yogurt sauce.
Meanwhile, season salmon with salt and pepper, set aside. Zest 1 teaspoon lemon; cut lemon in half and add 1 tablespoon juice to a mixing bowl. Cut remaining lemon into slices and set aside. Add yogurt, Dijon, and 1/2 teaspoon salt to bowl and mix. Refrigerate until ready to serve.
Place sheet pan in oven and preheat to 250 degrees F. Wrap potato mixture in cloth and squeeze to remove excess moisture. Heat a large cast iron skillet over medium heat; add 1 tablespoon butter and 1 tablespoon olive oil. Add 1/4 of potato mixture and spread into a thin even layer. Cook until golden brown, 5 minutes, then flip and cook 1 minute more. Transfer pancake to the sheet pan and return to oven to keep warm. Repeat steps for remaining 3 pancakes. Add additional butter and olive oil as needed.
Heat cast iron skillet over high heat; add 1 tablespoon olive oil to pan. When pan is almost smoking, add salmon skin side up. Sear on each side for 4 minutes. Serve salmon over potato pancake and top with yogurt sauce, sprinkle of sea salt and chives.
This is a healthy, super tasty and easy to prepare salmon dish. If I am in a pinch for time I replace the potato pancakes with some slightly wilted garlic spinach. This enables me to remove the carb and up the nutrients. Its a great from recipe from Judy Kim that I found on delish.