In a large pot, saute the onions and garlic over medium heat with the cumin, ginger, and turmeric until onions are soft, about 5 mins.
Add in the potatoes and carrots along with the stock, bring to a boil over medium-high heat, then reduce heat to simmer until the potatoes and carrots are soft, about 30 minutes.
Blend soup until smooth, or smoothish if you prefer. I like to use an immersion blender, but you do you.
Add in lemon, coconut milk, and grated carrot. Stir, and bring back up to heat.
Top with some grated carrot if you'd like, and serve!