To make the sauce: 
In a small bowl combine the sour cream, lemon juice, dill and cucumber. Season to taste with salt and pepper and set aside.

Heat the oil in a 12-inch nonstick skillet over medium-high heat until the oil begins to smoke. Add the salmon to the pan and cook skin side down for about 5 minutes. Flip salmon and sear for another 3 minutes.

To make the potato salad:
Cook the potatoes until fork-tender, 20 to 25 minutes.  Drain potatoes, then cut into 8 pieces, leaving skin on.

In a small bowl, combine the sour cream, chives and mustard. Add the potatoes to the bowl and fold slowly until all potatoes are coated.

Season to taste with salt and pepper. Sprinkle with dill and mix thoroughly.

Top salmon with dill sauce and serve with potato salad.