Mix potatoes and onion in medium saucepan. Cook and stir 5 minutes. Add chicken stock and stir in corn. Season with salt and pepper. Bring to a boil, reduce heat to low, and cover pot. Simmer 20 minutes, stirring frequently, until potatoes are tender.
Warm the milk mixture in a small saucepan until it bubbles. Remove from heat before it boils, and mix into the chowder just before serving.