Start the broth: Set a large soup pot on the stove over medium heat. Fill a kettle or a medium saucepan with water and bring it to a boil for the rice noodles.

Add the neutral oil to the large pot and let it heat for about 30 seconds.

Add the sliced onion and 1/2 teaspoon of the kosher salt to the pot. Cook for 4 to 5 minutes, stirring now and then, until the onion softens and looks glossy.

Add the ginger and garlic to the pot. Cook for 1 minute, stirring often, until they smell fragrant but are not browned.

Add the ground turmeric to the pot. Stir for 30 seconds so the spice blooms in the oil and colors the onions.

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

Bring the broth to a boil in the pot. This should take about 3 to 4 minutes.

Add the sliced cabbage and carrot matchsticks to the boiling broth. Stir to settle the vegetables into the liquid.

Lower the heat to medium and simmer the vegetables for 6 minutes. The cabbage should soften and the carrots should bend easily but still keep a little bite.

Soak the noodles: Put the rice noodles into a large heatproof bowl.

Pour the boiling water over the noodles until they are fully covered. Let them soak for 4 to 6 minutes, or until the noodles are tender but not falling apart.

Drain the noodles in a colander. Rinse them briefly with warm water and let them drain well so they do not keep cooking.