PREHEAT oven to 350º F. Grease 13 x 9-inch baking pan.
MICROWAVE 1 cup morsels in small, microwave-safe bowl on HIGH (100%) power for 1 minute; stir. Microwave at additional 10- to 20-second intervals, stirring until smooth. Cool to room temperature. Beat melted chocolate, sour cream, vegetable oil and eggs in large mixer bowl. Beat in sugar, flour, baking soda and salt.
DISSOLVE coffee granules in water; gradually beat into batter. Pour into prepared baking pan.
BAKE in oven for 40 to 45 minutes or until wooden pick inserted in center comes out clean.
SPRINKLE remaining morsels and nuts over warm cake. Cool completely in pan.