In a large pot, melt 2 tablespoons of butter over medium heat. Add 1 finely diced onion and 1 sliced leek, cooking for around 5 minutes until soft and translucent.

Stir in 4 cups of diced potatoes, ensuring they are coated with the buttery mixture. Sauté for an additional 3 minutes.

Pour in 4 cups of vegetable broth, increase heat to high until boiling, then reduce to a gentle simmer.

Add 2 cups of chopped green cabbage and 2 cups of kale, stir well, cover, and simmer for 15-20 minutes until potatoes are fork-tender.

Using an immersion blender, carefully puree the soup to your desired consistency.

Stir in 1 cup of milk, season with salt, pepper, and nutmeg, and heat gently for another 5 minutes.

Ladle the soup into bowls and garnish with sliced green onions. Serve immediately.