Add oil to a large pan, adding onion & leek when hot. Stir while cooking over a medium heat until onions are soft and translucent. Add stock and optional garlic. Add potatoes and cauliflower and bring to boil.
Reduce heat and simmer for approx 40-50 minutes. Add seasoning to taste.
Remove from heat and allow to cool a little before blending. (I use a hand blender but the choice is yours). When thoroughly blended, (seive if you wish) add cream and return to the heat to simmer for approx 5 mins.
Serve with crusty, buttered bread
The stock/water amount is approximate. More can be added depending on personal preference. The soup is best medium thick and can be frozen to use later.