Cook potatoes in boiling water for 8 to 12 minutes until just tender. Drain and cool.
Slice off the bottom end of each potato so it sits upright and slice off a third of the top. If potatoes are small/medium, cut them in half and use both halves.
With a melon baller, scoop out the potato and fill with a dollop of sour cream.
Top with walnut halves and tuck in a sprig of dill. Serve.