Preheat oven to 180 degrees C. Grease and flour a sheet pan. In a saucepan combine coffee, 250g butter and 5 tablespoons cocoa. Bring to a boil, reduce heat and stir until smooth. Remove from heat and set aside.
In a large bowl combine flour, white sugar, bicarb soda and salt. Make a well in the centre and pour in eggs, sour cream and 1 teaspoon vanilla. Mix well then beat in cocoa mixture. Spread into prepared pan.
Bake in the preheated oven for 20 to 25 minutes, or until a toothpick inserted into the centre of the cake comes out clean. Ice while still warm.
To make the icing: In a saucepan combine 125g butter, milk and 6 tablespoons cocoa. Bring to a boil, reduce temperature and stir until smooth. Remove from heat and blend in the icing sugar. Stir in 1 teaspoon vanilla and chopped pecans. Spread on cake while still warm.