Set the Instant Pot to ‘saute’ mode and add the butter to the pot. Once melted, add the leeks to the pot and cook for 4-5 minutes, until soft and wilted. Add the garlic and cook for an additional minute, until fragrant, then turn off the pot.
Add the chicken stock to the pot and scrape the browned bits off the bottom, then add the cauliflower, thyme, and salt. Seal the pot then hit the ‘manual’ button and set to cook for 5 minutes.
After the timer goes off, release the pressure from the pot. Either use your immersion blender to blend the soup in the pot, or add it to a blender, working in batches if needed, and blend until smooth.
Add the blended soup back to the pot and stir in the coconut milk and lemon juice. Taste for seasoning and add more salt if needed, then serve.
To Make This Soup on the Stovetop:
Follow step one over medium heat on your stovetop, then add the chicken stock, cauliflower, thyme, and salt. Cover and cook for 15 minutes on low heat, then proceed with steps 3 and 4.