Heat oven to 350 degrees F. Coat 13 x 9 x 2-inch baking pan with nonstick cooking spray. In small bowl, dissolve coffee powder in boiling water.
In bowl, mix flour, baking powder, salt and baking soda.
In large bowl, beat butter, sugar and egg on medium speed until creamy, 2 minutes. On low speed, beat in flour mixture, alternating with the coffee, beginning and ending with flour mixture. Stir in walnuts. Spread in prepared pan.
Bake in 350 degree oven 25 minutes, until wooden pick inserted in center comes out clean. Sprinkle mini chips over top. Bake 1 minute. Remove from oven; spread melted chips evenly over top. Cool in pan on wire rack.
Cut into 1-1/2-inch squares. Drizzle with white chocolate. Makes 40 squares.