Coat the bottom of a large pot with 1 tablespoon of olive oil and place it over medium heat.
Give the oil a minute to heat up, and then add the leeks, carrots, and celery.
Cook the veggies, stirring frequently until they begin to soften up, about 10 minutes.
Add the garlic and cook it for about 1 minute, until very fragrant.
Sprinkle the flour into the pot. Stir it well to form a paste that coats the veggies. Continue stirring and cooking the mixture for about 2 minutes.
Stir the beer and thyme into the pot. Raise the heat and bring the beer to a simmer.
Cook the beer and veggies at a low simmer for about 5 minutes, until the liquid reduces by about half, stirring frequently and scraping the bottom of the pot with a spoon to prevent the veggies and to stick
Stir in 1/2 of the broth. Raise the heat and bring the liquid back up to a simmer.
Allow the mixture to simmer for about 10 minutes, stirring occasionally, until the veggies are soft.
While the soup simmers, prepare the croutons.
When the soup has finished simmering remove the pot from the heat.
Place the cashews into the bowl of a food processor with 1/4 cup of the remaining vegetable broth.
Blend the cashews to a smooth paste, stopping to scrape down the sides of the bowl as needed, and drizzling in additional broth as needed.
Ladle all the veggies from the pot into the food processor bowl, and then blend them with the cashew mixture until smooth.
Add the cashew-veggie mixture to the pot, along with any remaining vegetable broth. You can also thin the soup with extra broth or water if you'd like.
Stir in the nutritional yeast, Worcestershire sauce, hot sauce, and mustard.
Place the pot back over medium heat and bring it back up to a simmer while stirring.
Once it gets to a simmer, remove the pot from the heat.
Season the soup with salt and pepper to taste. Be generous with the salt — it will help make the soup taste cheesy.
Ladle the soup into bowls and top with chives and croutons. Serve.