Lightly Grease an 8 inch/ 20 cm shallow square cake pan and line the bottom with parchment.
Preheat oven at 350 degrees Fahrenheit (180 C).
Place butter, sugars, chocolate, and corn syrup in a heavy based pan and heat gently, stirring until the mixture is well blended and smooth (or heat carefully in microwave).
Remove from heat and let cool.
Beat together eggs and extract. Whisk in the chocolate mixture.
Strain together the flour, cocoa, and baking powder; fold carefully into the egg and chocolate mixture using a metal spoon or spatula.
Spoon the mixture into a prepared pan and bake in a preheated 350 degrees Fahrenheit oven for 25 minutes or until the top is crisp and the edge of the cake is beginning to shrink away from the pan. The inside of the cake mixture will still be quite stodgy and soft to the touch.
Let the cake cool completely then cut into squares to serve.
Brownies can be well wrapped and frozen for up to 2 months. Thaw at room temp for about 2 hours or overnight in the fridge.