Dice the onion into 1/4-inch pieces and chop the celery. Peel and cut potatoes into 1-inch cubes, then trim the woody ends from asparagus and separate the tips from the stems (cutting stems into bite-sized pieces). Slice mushrooms into 1/4-inch thick pieces. Heat a large pot over medium heat with just enough water to cover the bottom, then add celery and onion, stirring occasionally until softened, about 5-7 minutes. This initial sauté begins building flavor depth even without oil.

Add the cubed potatoes and asparagus stems to the softened celery and onion. Pour in the soy milk and vegetable broth. Stir in the nutritional yeast, garlic powder, smoked paprika, salt, black pepper, and dried thyme until well combined. Bring the mixture to a simmer, then cover and cook for 10-15 minutes until the potatoes are completely tender when pierced with a fork. This gentle simmering allows the flavors to meld while the vegetables soften.

While the soup simmers, heat a skillet over medium-high heat and add the sliced mushrooms without any added fat (they'll release their own moisture). Cook for 5-7 minutes, stirring occasionally, until the mushrooms are tender and lightly browned. Add the reserved asparagus tips to the skillet and cook for another 2-3 minutes until they turn bright green and are tender-crisp. I prefer keeping the mushrooms and asparagus tips separate until the end so they maintain their texture and visual appeal in the finished soup.

In a small bowl, whisk together the flour with a few tablespoons of cold water until completely smooth with no lumps. Once the potatoes in the soup are tender, slowly pour the flour mixture into the pot while stirring constantly to prevent clumping. The flour will thicken the broth and create a creamy base without any dairy.

Carefully transfer the hot soup to a blender in batches (or use an immersion blender directly in the pot for easier cleanup). Blend until completely smooth and creamy, about 1-2 minutes per batch. Return the blended soup to the pot and bring it to a gentle simmer over medium heat, stirring occasionally, for 2-3 minutes to ensure it reaches the desired thickness and temperature. Stir in the fresh lemon juice to brighten the flavors. I like to add the lemon juice at this final stage—it's a small touch that makes the earthy mushroom and asparagus flavors really pop.

Gently fold the cooked mushrooms and asparagus tips from Step 3 into the blended soup, stirring carefully to incorporate them without breaking them apart. Ladle the soup into bowls and serve immediately while hot. The mushrooms and asparagus tips will float beautifully on top, adding texture and visual contrast to each spoonful.