In a large soup pot or Dutch oven, melt 4 tablespoons (60 ml / 2 fl oz) of butter over medium heat.
Add the sliced carrots and chopped onion, and sauté for 5-7 minutes until they begin to soften.
Stir in the sugar, 1 teaspoon (5 ml / 0.2 fl oz) of salt, the diced potato, and the water.
Bring to a simmer, then reduce the heat to low, cover tightly, and cook for 15-20 minutes, or until the vegetables are very tender.
Carefully transfer the cooked vegetables and any liquid to a blender.
Add the light cream and blend until completely smooth and velvety. You may need to do this in batches depending on the size of your blender.
In a separate skillet or the now-empty soup pot, melt the remaining 4 tablespoons (60 ml / 2 fl oz) of butter over medium-low heat.
Whisk in the flour to form a paste (a roux) and cook for 1-2 minutes, stirring constantly, until it turns a light golden color.
While whisking continuously, slowly pour the warm milk into the roux.
Continue to cook over low heat, stirring often, until the white sauce thickens and coats the back of a spoon, about 5-8 minutes.
Pour the carrot purée into the pot with the white sauce and stir to combine.
Season with fresh black pepper, paprika, and a pinch of cayenne. If using, add the minced garlic and brandy.
Taste and adjust the salt as needed.
Gently simmer the soup over low heat for 10-15 minutes, stirring occasionally to allow the flavors to meld.
Do not let it boil.
Serve the soup hot, garnished with homemade croutons or a sprinkle of fresh chopped parsley.
