Place the olive oil in a large stock pot and turn the heat to medium.
Add the leek and garlic, season with salt and pepper, and allow to cook until leeks are soft and garlic is fragrant, about 3 minutes.
Add carrots, celery and kale, stir to combine, then add dried thyme and red pepper flakes, and allow to cook for about another 7 minutes or until carrots are softening up.
Add the white beans with their soaking liquid and stir to combine, then add stock.
Bring to a boil, then lower heat to a vigorous simmer and allow to cook and reduce with the lid off for about 25 minutes.
Taste and season with more salt and pepper if desired; ladle into bowls and serve hot.