1) Heat the oil in a large stockpot set over medium-high heat, until it shimmers.

2) Add the leeks, garlic, and celery, and cook, stirring frequently, for 3 to 4 minutes, until the edges are golden.

3) Add the parsnips, potatoes, cabbage, kale, stock, salt, and pepper and stir well. Reduce the heat to medium and cover.

4) Bring the soup to a boil; then reduce the heat to a low simmer. Cook for 30 to 35 minutes, until the vegetables are tender and soft.

5) Add the lemon juice.

6) Using an immersion blender (or working in batches in a blender), pure until completely smooth.

7) Serve immediately or store in an airtight container for up to 3 days.