You can use pot or pearl barley in this soup. Pot barley will take a bit longer to cook, so add 30-35 minutes to the cooking time if you use it. Sumac is a slightly sour spice that provides a nice contrast in this soup. If you don't have any, you can omit it or add 1/2 tablespoon / 7.5 ml of lime or lemon juice to the soup at the end of the cooking time.
Heat a large saucepan over medium-low heat. When the pan is heated, add oil and swirl to coat pan. Add onions and cook until soft, about 3-5 minutes. Don't let the onions brown. If they start to brown turn down the heat. Add garlic and cook for 1-2 more minutes.
Add 1/2 teaspoon of salt and chili powder. Stir to coat onions with spices and cook, stirring for one minute. Add tomato paste and cook for another minute.
Add barley and vegetable stock. Bring soup to boiling, then reduce heat and cover. Simmer for 30 minutes (if you are using pot barley, simmer for an additional 30 minutes), stirring occasionally to prevent sticking.
Add pumpkin, salt, ground pepper and sumac (if using). Stir until smooth and simmer for an additional 15 minutes, stirring frequently to prevent soup from sticking.
Test a barley grain. They should be a bit chewy, but not hard. Serve hot, or let cool and refrigerate for up to 3 days or freeze. The barley will continue to soften as the soup cools.
If you are making this soup ahead of time, you may need to thin it out as the barley will continue to thicken the soup during cooling. Add 1/2-1 cup / 125-250 ml additional stock
Pearl barley vs. pot barley: Pearl barley is polished and slightly more refined than pot barley, however it retains most of the same nutritional value. Pot barley will require additional cooking time in order to soften.
To freeze: Cool soup and freeze for up to 2 months. Thaw in fridge, then reheat on stovetop or in microwave.