Slice leeks into ¼ inch half rounds. Heat oil in medium sized heavy bottom pot or dutch oven, over medium heat. Add leeks ( or onion) and sauté until tender and golden, about 7-8 minutes. Continue. Add garlic and sauté for 3 more minutes.
Add diced cauliflower (remember the smaller you cut these, the faster this will cook) veggie stock, salt and fresh sage. Give a stir. The liquid will not cover the cauliflower at first, but don’t worry it will steam. Bring to a boil, cover, turn heat to medium low and simmer for 10-15 minutes, until cauliflower is very tender.
Blend using a submersion blender, or if using a regular blender, blend in batches, for 30 seconds, until very smooth and silky —remember, you don’t want to fill up a blender with hot liquid, or you will have a soup explosion — so blend in small batches, less than half full, with the lid covered with a kitchen towel and held down firmly with one hand when you start the blender.
Return the creamy smooth soup to the pot, over low heat, and stir in the sour cream. Add pepper and adjust the salt.
To make the Pine Nut crumble, place all ingredients (except butter) in food processor and pulse several times until it is roughly chopped. Heat butter (or oil) in a skillet over medium heat and gently toast the crumble, stirring constantly for about 5 minutes until golden and fragrant. Season with salt and pepper.
Divide soup among bowls and sprinkle with the pine nut crumble.
Feel free to add soaked cashews to the blender with the soup for a tasty vegan option. The sour cream adds a subtle tanginess, so if needed, add a few drops of lemon or AC vinegar ( be conservative).