Combine flour, baking powder, baking soda and salt in a large bowl and set aside
Combine sugar, butter, corn syrup and espresso in a saucepan and heat until sugar is dissolved
Add chocolate squares and continue heating over low heat until chocolate melts be careful not to scorch
Add chocolate mixture to flour mixture and mix with a hand mixer
Add eggs and vanilla and mix again
Pour batter into a greased 13 x 9 inch baking pan and cook at 325 degrees for about 45 minutes
Allow to cool and cut into squares to serve