Preheat oven to 190°C (375°F) degrees. Scrub the beetroot clean, slice off the top, sit it in enough aluminium foil to wrap around it, drizzle with olive oil, sprinkle the salt on, and wrap the foil tight around the beetroot so it’s completely sealed.
Roast the beetroot for 30 minutes, then check if it’s done by piercing it with a wooden toothpick or skewer. If it slides in easily and the beetroot feels tender, it’s ready. If it doesn’t, pop it back in the oven for another 5-10 minutes and check again, then pull the beetroot out to cool.
When the beetroot is cool enough to touch, rub the skin off with paper towels or peel with a vegetable peeler or paring knife, then julienne or grate the beetroots into small thin slices into a large bowl. (Wear gloves if concerned about stained hands.)
Dice the cucumbers, slice the scallions or green onions, roughly chop the fresh dill, and add all to the large bowl the grated or julienned beetroot is in.
To the same large bowl, add the water and kefir (or buttermilk), salt and pepper, stir to combine well, and taste. Add additional salt and pepper if needed to suit your palate.
Cover the bowl and refrigerate the soup to chill until you're ready to serve. If you're not eating for a while, transfer it to a container with well-fitted lid. When cold, ladle into big bowls if serving for lunch for two, or smaller bowls as an appetiser for four, or shot glasses for an amuse bouche. Garnish with a dollop of sour cream and fresh dill and boiled egg halves if you like.