Slice cucumbers and onions then add them to a medium bowl. Set aside.
In a small bowl combine the sour cream, sugar, vinegar, salt and pepper, whisk well.
Pour the dressing over the onions and cucumbers and mix well. Serve right away or store in the fridge for an hour before serving.
Notes
Best served immediately. Store in an airtight container for up to 2-3 days. If too much water accumulates from the cucumbers, pour it off and add more sour cream before serving.