Preheat your oven to 180C (160C fan / 350F).

Put the soft brown sugar and lemon zest in a bowl and rub together to release the lemon oils. (Pop the zested lemons in the fridge as you'll need them later.)

Add the flour and baking powder and mix together until smooth - the batter may be quite liquid if the butter was warm, but that's fine.

Add the white chocolate chips.

Pulse the pistachios in a food processor for about 8-10 seconds, so that you have some finer crumbs and some larger pieces.

Fold the pistachios into the batter.

Spoon into a lined baking tray.

Bake for 24-26 minutes until firm at the edges and a little under in the centre - it will continue to set as it cools.

Place the tin on a wire rack and allow to cool complete, then pop in the fridge for a couple of hours or overnight until completely firm.

Lift the blondies onto a serving board, remove the baking paper and slice into 15 squares (in a pattern of 3 by 5).