DO-AHEAD TIP: Cook and crumble bacon.
Heat the olive oil in a large saucepan with a tight-fitting lid over medium heat. Add leeks and garlic; sauté for 5 minutes.
Add carrots and celery; cook for 3 to 4 minutes. Reduce heat to low then add flour; cook and stir for 2 to 3 minutes. Add clams and their juices, potatoes, wine, fish stock and thyme; cover and simmer for 1 hour. Add corn; cook for 5 minutes or until heated through then salt and pepper to taste.
Ladle chowder into bowls and garnish with chopped parsley and crumbled bacon.