Melt butter in a large heavy saucepan or Dutch oven over medium-high heat.

Add chicken pieces and cook until browned on all sides, turning occasionally.

Season with 1/2 tsp salt and pepper.

Add chicken stock, baking potatoes, green onions, cilantro, guascas, and remaining 1 tsp salt.

Reduce heat to low, cover, and simmer for 30 minutes, or until potatoes are tender.

Remove chicken and baking potatoes from stock with a slotted spoon; cover to keep warm.

Strain stock through a sieve and return stock to the saucepan.

Discard the strained vegetable pieces.

Add papas criollas, red potatoes, corn, and milk to the saucepan.

Simmer for 35 minutes, or until potatoes are almost tender.

Return chicken and baking potatoes to the saucepan.

Add capers and simmer for 10 minutes, or until the stew is heated through.

Remove from heat and stir in sour cream.

Serve in deep soup bowls topped with chopped hard-cooked eggs.