Preheat an oven to 375°F (190°C).
Stick 1/2 garlic cloves in the flesh of each squash piece. Place the pieces flesh-side down in a baking pan or ovenproof dish. Pour in the boiling water. Place in the oven and bake until tender when the flesh is pierced, about 1 hour, adding additional boiling water if the pan begins to dry. Remove from the oven and leave the squash in the pan until cool, 20 - 25 minutes. Discard the cloves and scoop out the flesh; you should have about 5 cups (2-1/2 lb. - 1.25 kg). Set aside.
In a large saucepan over low heat, melt the butter. Add the onion and marjoram, cover and cook over very low heat until translucent and tender, 15 - 20 minutes. Remove from the heat.
In a food processor fitted with the metal blade, combine the squash and onion-marjoram mixture. Process to a smooth purée. Return the purée to the saucepan and stir in the stock and lemon juice. Cook over medium-low heat, stirring frequently, to blend the flavors, 8 - 10 minutes. Do not allow to scorch. Season to taste with salt and pepper.
Just before serving, stir in the cream and heat almost to a boil. Ladle into soup bowls and top with a dollop of sour cream and a grating of nutmeg or a sprinkling of parsley or mint.