Pre-heat the oven to 180°C/160°C fan assisted/gas mark 4 and line and grease a 20cm square baking tin.
Brown the butter by melting the butter in a small saucepan over a medium heat. Once melted the butter will start hissing and cracking and forming little brown bits at the bottom of the pan. Wait until the noises start to subside and the butter smells toasty Remove from the heat straightaway and pour into a heatproof mixing bowl so it doesn’t begin to burn.
Stir the sugars into the butter, followed by the eggs and vanilla extract.
Sift the flours together, in a separate mixing bowl, with the baking powder, coffee powder and salt.
Beat the flour mix into the wet ingredients until completely combined.
Fold in the chopped white chocolate and pecans and pour the batter into the baking tin.
Bake for 30 minutes then leave in the tin to settle for 10 minutes.
Remove from the tin and leave to cool on a cooling rack before cutting into 12 bars.