Peel and chop the potatoes into 2.5 cm (1 inch) cubes, ensuring they are roughly uniform for even cooking.
Heat the olive oil in a large pot over medium heat. Add the chopped onion and sauté until translucent and fragrant, about 5 minutes, with a gentle sizzle and a sweet aroma filling the kitchen.
Add the chopped potatoes to the pot, stirring to coat them in the oil and onion mixture. Cook for another 2 minutes until slightly starting to soften.
Pour in the vegetable broth, ensuring the potatoes are submerged. Drop in a bay leaf if using, and season with a pinch of salt. Bring the mixture to a gentle boil, hearing the bubbling sound as the broth heats.
Reduce the heat to low, cover the pot, and simmer for about 15-20 minutes until the potatoes are fork-tender, with a soft, yielding texture and the aroma of cooked onions and potatoes filling the air.
Remove the bay leaf and use an immersion blender directly in the pot to blend the soup until it’s smooth and velvety, or transfer carefully to a blender and purée until silky, then return to the pot.
Stir in the nutritional yeast and cook for another 2 minutes, allowing the flavors to meld and the soup to thicken slightly. Adjust seasoning with salt and pepper to taste, and add a squeeze of lemon juice if you like a bright finish.
Taste the soup, adjusting salt and pepper as needed. The soup should be creamy, smooth, and warm, with a comforting aroma ready to serve.
Serve hot, garnished with fresh herbs or a drizzle of olive oil if desired. Enjoy this cozy, nourishing bowl that’s perfect for chilly days.