Cut off roots and trim leaf ends of leeks. Slice each leek lengthwise in half. Separate leaves and rinse under running water. Cut crosswise into 1/2″ pieces.
Peel and clean garlic cloves. Dice finely. Rinse celery and cut into 1/2″ pieces. Rinse matchstick carrots. Rinse baby red potatoes and slice each in half.
Cut chicken breasts into 1 1/2″ pieces.
In a 5 quart Dutch oven, heat one tablespoon of the olive oil until hot over medium high heat. Add one tablespoon of butter and melt.
Add cut up chicken and cook until chicken is lightly browned and no longer pink, about 15 minutes. Remove chicken with a slotted spoon to a medium bowl. Set aside while you prepare the vegetables.
To the Dutch oven, add the remaining tablespoon of olive oil and the remaining tablespoon of butter. Melt. Add leeks, carrots, celery, garlic and potatoes.
Season with sea salt, black pepper, oregano and rosemary. Cook and stir until vegetables are lightly browned and leeks soft, about 10 to 15 minutes.
Add wine and chicken broth. Heat to boiling over high heat. Reduce heat to medium high and cook until potatoes are tender, about 20 minutes.
In a small bowl, whisk together cornstarch and milk. Reduce heat to medium and stir into vegetable mixture, stirring constantly until thickened.
Stir in chicken and peas. Simmer over low heat until heated through.
Serve with a crisp green salad and French bread.