1 Dice the leeks as shown in the video.
2 Finely chop the sweet onion.
3 In a large pan, melt the butter and add the sweet onion along with a pinch of salt.
4 Cook for about 40 minutes, stirring occasionally.
5 Meanwhile, wash the leeks thoroughly and strain.
6 Peel and dice the potatoes and set aside.
7 At this stage, check the onions if they have carmalized.
8 Add in the flour and simmer for about 3 minutes to prepare the roux.
9 Gradually pour in 1 cup of chicken stock or vegetable stock, stirring constantly.
10 Now add in the remaining stock, stirring, until all the liquid is incorporated.
11 Add the potatoes and leeks, at this stage you can add your other favorite vegetables too.
12 Simmer for 40 to 50 minutes.
13 Blend well using a stick blender.
14 Season to taste with salt and pepper.
15 Add a touch of dry white wine for added flavor (optional)