1/4 cup butter
1 large yellow onion, chopped
2 leeks, white and pale-green parts only, rinsed and coarsely chopped
4 cloves garlic, smashed
1 stalk celery, cut into chunks
4 cups vegetable stock
5 potatoes, peeled and cubed
1 cup vegetable stock
1 1/4 cups sliced baby carrots
3 tablespoons chopped green onion
3/4 cup heavy cream
salt and ground black pepper to taste