Heat the olive oil in a large saucepan over medium-high heat.

Add the sweet potatoes, baby potatoes, garlic, ginger, and red onion.

Cook for 5 minutes, stirring frequently.

In a measuring cup, whisk together the lemon juice, tahini, tamari, nutritional yeast, cayenne pepper, and 2½ cups (590 ml) of water.

Pour the mixture into the saucepan.

Bring to a boil, then cover and reduce to a simmer for 15–20 minutes, until the potatoes are tender but firm.

In a separate bowl, whisk the remaining 1 cup (235 ml) of water with the miso.

Add the miso mixture and frozen spinach to the saucepan, stirring well.

Do not let the soup return to a boil to preserve the miso's health benefits.

Let simmer for another 5–10 minutes, or until heated through.

Use an immersion blender or countertop blender to purée the soup until smooth.

For texture, you can leave some chunks by partially blending it.