Curry Oil: In a small bowl, combine the curry powder and canola oil, and mix well. Repeat two more times, then stain through a coffee filter or moistened paper towel. The curry oil can be kept in the refrigerator upto three month, in an air tight container.
Barley: In a large, heavy saucepan, melt the butter. Add the onion and garlic and cook for a few minutes, until the liquid evaportes, about five minutes. Add the barley and mix well. Add enough water to cover the barley by 2 inches and bring to a boil. Reduce the heat and simmer untilt he barley is al dente, about 25 minutes. Add more water as needed. Once the barley is cooked, drain it in a colander and rinse under cold water to stop the cooking. Leave the barley in the colander set over a bowl for the excess water to drain. Reserve 1 ½ cups of the cooked barley for the soup.(See Note Below) The barley could be made upto three days before and kept covered in the refrigerator.
Yogurt and Egg Mixture: In a medium bowl, whisk together the yorgurt and egg yolks, then incorporate the milk and cream. This could be prepared and kept in the refrigerator upto three days in advance.
To Make the Soup: If the yogurt-egg mixture was chilled, take it our of the fridge and place it in a medium bowl, about 20 minutes before you want to make the soup.
In a heavy bottomed, medium saucepan, bring the stock of your choice and 1 ½ cups of the cooked barley to a simmer. Very gradually whisk one cup of the hot stock and barley mixture into the yogurt and egg to temper the mixture.
Gradually whisk the tempered yogurt and egg mixture into the saucepan of stock and barley and bring to a gentle simmer. Don’t let it boil or the egg will curdle.
Season the soup with salt and pepper. Add the herb mixures and the currants if using, mix well. Squeeze the juice of half a lemon and taste; if needed, add more lemon juice.
Laddle the soup into soup bowls, drizzled with a bit of the curry oil and serve.
NOTE: Since the soup only calls for1 ½ cups of the cooked barley, I make a salad with the leftover barley by tossing it with chopped herbs and finely diced carrots and parsnips and dress it with olive oil and lemon juice. You could also add any variety of vegetables or greens to the barley salad.