Heat 2 tablespoons of the oil in a stockpot over medium-high heat.
Add chicken stock, tarragon, salt, pepper, and bring to a boil.
Reduce the heat to low, cover and simmer until squash and apples are tender - about 50 minutes.
When the apples and squash are tender, puree soup using an immersion blender.
Taste, and adjust seasonings as necessary.
If garnishing with fried leeks, saute the leek rounds in about 1 tablespoon olive oil, for about 5 minutes, or until they just start to turn golden.
Ladle soup into bowls, and if desired, garnish with fried leeks and pepitos