In a large saucepan, heat the olive oil over medium-high heat.

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

Cook for 5 minutes, stirring often.

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

Add this mixture to the vegetables in the saucepan and bring to a boil.

Cover with a lid and let simmer for 15 to 20 minutes, until the potatoes are tender but still firm.

Whisk together the remaining 1 cup (235 ml) of water and the miso.

Add this to the saucepan along with the spinach.

Stir well, but do not bring the soup back to a boil, as this can diminish the health benefits of miso.

Let simmer for another 5 to 10 minutes until the potatoes are to your liking and the soup is heated through.

Using an immersion or countertop blender, purée the soup until smooth, or leave some chunkiness by removing some soup and blending it partially.