In a pot heat the butter over low heat. Add the onion to the melted butter, followed by potatoes, and sauté stirring until the onions start to become translucent.Add 3 tablespoons of vegetable or chicken broth and cover with a tight-fitting lid. Simmer until the potatoes are cooked through, stirring and adding broth by the tablespoon as it becomes necessary.Add the remaining broth and the broccoli. Increase heat to medium and bring to a boil. Once it has come to a rolling boil, remove it from the heat. Let the preparation cool to room temperature.
Step 2: Blending the soup
Pour into the blender vase and add the rest of the broth, milk, salt, pepper, cream cheese, and mozzarella or white cheddar.Blend the soup with an immersion blender or regular blender.
Step 3: Reheating the soup
Pour the liquefied soup into the pot, and return to the stove over medium-low heat bring it to the boil. Taste and add salt to taste if you find it necessary.Remove from the heat and serve. Sprinkle with parmesan.
Cook's notes
For a low-carb version, substitute arracacha (cepa de apio) for potato. You can also use russet potatoes if you don't have Yukon gold.For extra creaminess, substitute whole milk for heavy cream.If you prefer a stronger taste, substitute sharp cheddar cheese for the mozzarella.