Preheat oven to 350*F (175*C). Grease
a 15 x 10 x 1-inch jelly roll pan; set aside.
To prepare bottom layer, combine flour,
sugar, baking powder and salt in a large mixing bowl. Cut in
butter until mixture resembles coarse crumbs.
In small bowl, mix coffee and egg yolk
to blend; stir into flour mixture to moisten evenly.
Form dough into a roll. With floured fingertips,
press evenly onto bottom of prepared pan. (Layer will be thin.)
Bake for 10 minutes.
Sprinkle chocolate pieces evenly over
crust; return to oven 2 minutes to melt chocolate. Remove from
oven; spread evenly with spatula. Allow to stand several minutes
to set.
To Prepare top layer, cream butter, sugar
and vanilla in large mixing bowl. Beat in eggs and egg white,
one at a time, mixing well after each addition. (Mixture will
appear slightly curdled.)
Stir in raisins and walnuts. Spread evenly
over chocolate layer. Return to oven; bake 20 to 25 minutes or
until top is browned.Cool completely in pan on wire rack.
Dust with powdered sugar, if desired.
Cut into bars.
