Saute aromatics: Warm 2 tablespoons extra-virgin olive oil in a large pot over medium-high heat. Add 1 diced yellow onion and saute until translucent, about 3 minutes. Add 3 cloves minced garlic, 1 teaspoon dried thyme, and ½ teaspoon fine sea salt. Cook, stirring continuously, until fragrant, about 1 minute.
Boil: Pour in 6 cups vegetable broth, then stir in 1½ cups grated potato. Cover with the lid slightly ajar and bring to a boil. Boil for about 10 minutes (potato should be soft). Add 2 lbs frozen peas and cook until they're bright green and warmed through, 2 to 3 minutes. Remove from heat. Stir in 4 cups baby spinach (if using), until wilted.
Blend: Carefully use an immersion blender to blend soup until smooth, or use a blender (in batches). Season with Black pepper (to taste) and more salt if needed. Garnish, if desired (see note 3).
