How to Make the Ultimate Umami-Bomb Vegetarian Demi-Glace
2 tablespoons unsalted butter
4 leeks, white and tender green parts only, coarsely chopped
1 celery rib, chopped
1 garlic clove, smashed
1 quart chicken stock, preferably homemade
1 large butternut squash, peeled and cut into 1/2-inch dice (3 cups)
1 tablespoon tomato paste
1 large bay leaf
Sea salt and freshly ground pepper
1/4 cup flat-leaf parsley leaves
1/2 cup heavy cream
Melt the butter in a large heavy saucepan. Add the leeks, celery and garlic and cook over moderate heat, stirring occasionally, until softened, 7 to 8 minutes. Add the stock, squash, tomato paste and bay leaf. Season with salt and pepper and simmer over moderately low heat until all the vegetables are tender, about 25 minutes. Discard the bay leaf and add the parsley.
Puree the soup in a blender, then return it to the saucepan. Stir in the cream and cook just until heated through. Season with salt and pepper and serve.