In a preheated medium size pot add oil, onion, garlic, leek and fennel saute for 5-8 min to soften vegetables. Sprinkle with salt & pepper. Add diced potatoes and continue stirring and cooking on medium heat for another 5min.
Add broth and bring pot up to boil. Immediately turn down the heat to a simmer and cook until vegetables are fork tender. Approx. 20-30min. Taste for seasoning.
Using a slotted spoon transfer the larger chunks of vegetables to a blender add some stock just to blend and puree.
I like leaving a few chunks to add texture so everyone can see the ingredients.