Rinse the grated potatoes in cold water until the water is clear. Drain well, squeeze out the excess moisture, thoroughly dry on a paper towel and place in a bowl. Mix in the remaining pancake ingredients, except the oil.
Line a baking sheet with parchment paper. Heat a thin layer of vegetable oil in non-stick skillet or griddle over medium, medium-high heat.
Working in batches, set compacted, 1 1/2” to 2” inch wide, 1/2” thick rounds of the potato mixture on the cooking surface. (Be careful not to overcrowd the pancakes in the pan when cooking, or they’ll be difficult to flip.)
Cook the pancakes 2 to 3 minutes per side, drain on paper towel and set on the baking sheet. Finish cooking the rest of the potato mixture in this fashion.
Make a sauce for the pancakes by combining the sour cream, mayonnaise and mustard in a small bowl.
Arrange the pancakes on a serving tray. Top each pancake with a small spoon of the sauce. Set 1 or 2 slices of salmon on each pancake, and then top the salmon with a bit more of the sauce and a dill sprig, and then serve.
Note: Pancakes can be made several hours in advance, cooled, and kept wrapped in the fridge until needed. Warm to room temperature or heat in a 200 degrees F oven before topping.