Locro is a common word for a thick soup/stew in the Andes. This particular version, 'de papa', is potato-based. The key to its creaminess is using starchy potatoes (like Russet) which partially dissolve into the soup, and adding milk and cheese at the end.
Achiote (annatto) is crucial for the authentic color and subtly earthy flavor. If unavailable, substitute with a pinch of turmeric and paprika.
In a large pot over medium heat, heat the olive oil. Add the diced onion and cook for 4-5 minutes until softened.
Add the minced garlic, achiote, and cumin. Cook, stirring constantly, for about 1 minute until fragrant (the achiote will give the oil an orange-red color).
Add the potatoes and mix so they are coated in the spice base. Cook for about 5 minutes, stirring occasionally.
Pour in the broth (or water) and add 1 tsp of salt. Bring to a boil, then reduce heat, cover, and simmer until the potatoes are very tender and some are starting to break down (about 20–30 minutes).
Remove the lid. Use a potato masher or an immersion blender to partially mash/blend the soup. The goal is for about half of the potatoes to break down, creating a creamy texture, while the other half remains in chunks.
Add the milk and return the pot to medium-low heat. Stir until the soup is heated through, but do not boil.
Remove the pot from the heat. Stir in most of the grated or crumbled cheese (queso fresco). Stir until the cheese has melted and the soup has thickened and gained a creamy sheen.
Season with salt and pepper.
Serve the Locro de Papa hot. Garnish each bowl generously with diced fresh avocado, the remaining cheese, chopped cilantro, and hot sauce if desired.