To prepare the sour cream dip, combine all the ingredients in a bowl and mix well. Chill for at least 1 hour before serving.
With a fork or a channelling knife, scrape down the length of the cucumber to create a ridged pattern, then cut into 5 mm (¼ inch) slices. Cut the celery and capsicums into 5–8 cm (2–3 inch) long sticks. Blanch the broccoli, corn, snow pe