Leek and potato soup

Leek and potato soup, or rather my take on it: More leeks less potato.
For this I have followed a few tips from the Tim Spector's latest book "Food for Life: The New Science of Eating Well"
I reduced the ratio of potatoes to leeks to make it less heavy on carbs and more nutritious. I also added fried crispy leeks to add fibre to the soup.
Here's the recipe for it;
Ingredients
50gr butter
500gr leeks, keep 1/2 a side and cut the rest in half and slice roughly
1 medium potato cut to 2cm cubes
1 litre vegetable stock
100ml double cream
Crispy fried leeks
1/2 preserved leek thinly sliced
Oil to fry
Method
Melt butter in a saucepan and add leeks and the potatoes. Cook them 2-3 minutes tossing to get everything coated with butter.
Add 1/2 teaspoon fine seasalt and generous grind of black pepper then toss again.
Wet a piece of kitchen towel with water, squeeze out the excess water and put it on top of the vegetables , then cover the pan with its lid.
Cook for 5 minutes on low heat.
Uncover the lid, take off the paper towel and add vegetable stock. Bring to boil and simmer for 5 minutes.
Purée with a stick blender until smooth and stir in the cream.
Pour enough vegetable oil into a small sauté pan so it rises 3cm up the sides of the pan once the oil is hot, carefully add the leeks in batches. Fry for 2 minutes stirring frequently to stop the leeks sticking together, or until golden brown and crisp.
Using a slotted spoon, transfer the leeks to a plate lined with kitchen paper and sprinkle with a pinch of salt. Continue with the remaining leeks in the same way, then set aside
Pour soup into bowls, top with crispy fried leeks and drizzle with olive oil.