Set a large pot on the stove over medium heat and add the olive oil.

Add the chopped onion, sliced carrots, and 1/2 teaspoon of the kosher salt to the pot.

Cook the vegetables for 6 to 8 minutes, stirring now and then, until the onion looks soft and the carrots have started to lose their raw crunch.

Add the sliced garlic and ground cumin to the pot.

Stir for 30 seconds to 1 minute, just until the garlic smells fragrant and the cumin is evenly coated in the oil.

Pour the vegetable broth into the pot and raise the heat to high.

Bring the broth to a boil, then lower the heat to medium-low so the soup bubbles gently.

Cook for 10 to 12 minutes, until the carrot slices are very soft and can be mashed easily with a spoon against the side of the pot.

Turn off the heat and blend the soup until smooth with an immersion blender right in the pot. If you use a regular blender, blend carefully in batches and pour the soup back into the pot when it is smooth.

Put the tahini into a small bowl and ladle in about 1/2 cup of the hot soup.

Whisk the tahini and hot soup together until smooth and loose, with no thick lumps left.

Stir the tahini mixture and the lemon juice into the pot of blended soup.