Savory Sundays: Slow Cooker Leek & Potato Soup

large leeks (, washed, ends trimmed, thinly sliced)

large russet potatoes (, peeled and quartered)

carrots (, washed and chopped)

celery stalks (, chopped)

garlic (, minced)

salt and pepper

to 6 cups vegetable broth (, or enough to cover the vegetables)

croutons and fresh parsley for garnish

heavy cream ((optional))