Place currants in small bowl. Add Sherry and let soak 2 hours.
Preheat oven to 350°F. Lightly butter 8-inch square baking pan. Melt 3 tablespoons butter in heavy medium skillet over low heat. Add onion and cook until translucent, stirring occasionally, about 4 minutes. Add flour and curry powder and stir 3 minutes. Gradually whisk in milk. Bring to boil, stirring constantly. Mix in currants with Sherry and apple. Season to taste with salt.
Arrange chicken in prepared pan in single layer. Cover with sauce. Top with almonds. Bake until chicken is cooked through, about 30 minutes.