2 tbsp extra-virgin olive oil
1 yellow or white onion diced
3 cloves garlic minced
1/4 tsp ground black pepper
1/4 tsp red pepper flakes
8 oz Yukon gold potatoes peeled and cubed (or other waxy potatoes)
16 oz kohlrabi peeled and cubed
4 cups low-sodium vegetable broth
1 bay leaf fresh herbs (optional, for serving)
Heat the olive oil, add the onion and salt, and cook with occasional stirring until the onion is opaque, 4 to 5 minutes. Add the garlic, black pepper, and red pepper flakes, and cook for another 60 seconds or until the garlic is fragrant.
Add the cubed potatoes and kohlrabi, stirring to combine, and cook for about 1 minute. Add the vegetable broth and bay leaf. Bring the mixture to a boil, then reduce it to a simmer. Continue to cook, stirring occasionally, until the kohlrabi and potatoes are tender, about 20-25 minutes.
Remove the bay leaf. Use an immersion blender to puree the soup until smooth; or transfer to a blender or food processor and puree in batches. Season to taste with additional salt, pepper, and olive oil; serve warm.