Set a large soup pot on the stove over medium heat.

Add the neutral oil to the pot and heat it for about 30 seconds, until it looks loose and shiny.

Add the chopped onion to the pot. Cook, stirring often, for 3 minutes, until the onion starts to soften.

Add the sliced mushrooms to the pot. Cook for 4 minutes, stirring now and then, until the mushrooms shrink and look lightly browned in spots.

Add the carrots to the pot. Stir and cook for 2 minutes so they start to soften at the edges.

Pour the vegetable broth and 2 cups water into the pot. Stir in the soy sauce.

Turn the heat up to high and bring the pot to a boil.

Lower the heat to medium so the broth stops splashing hard. Add the curry roux pieces to the pot.

Stir the pot until the curry roux fully melts into the broth and no firm pieces are left. The broth should look smooth, glossy, and deeper brown.

Bring the broth back to a gentle boil over medium-high heat.

Add the rice noodles to the pot. Use a spoon to press them down into the liquid as they soften.

Cook the noodles for 3 to 4 minutes, stirring often, until they separate and bend easily but are still a little firm in the center.