Melt butter in a medium saucepan over medium heat. Add shallots; cook until soft and translucent, about 2 minutes. Add ginger and curry powder; cook, stirring, 1 minute. Add apples, potato, salt and chicken stock. Bring to a simmer over medium-high heat, and cook until potato is tender when pierced with a paring knife, about 12 minutes. Remove from heat, and let cool slightly.