Wash leeks and finely slice the white and light green parts. Discard the dark green tops.

Heat 2 tablespoons extra virgin olive oil in a medium saucepan on a medium heat. Remove and discard stems from the thyme. Add chopped leeks and thyme to the saucepan. Cook, covered for about 10 minutes or until leeks are soft but not browned. Stir once or twice to make sure the leeks don't burn.

While the leeks are cooking peel celeriac (if using) and chop into 1cm chunks. If using cauliflower no need to peel :).

When the leeks are soft add the prepared celeriac / cauliflower, the stock and 1.5 cups water. Simmer uncovered for 15 minutes or until the veg are no longer hard and crunchy.

While the soups is cooking de-seed olives and chop the flesh. Coarsely chop the pecans.

When the soup is cooked, remove from the heat and carefully puree using a stick blender. Or leave the soup chunky if you prefer.

Divide hot soup between two bowls and top with olives, pecans and a drizzle of extra virgin olive oil.