01 -
Heat oven to 180°C / 350°F. Line a 20 cm square baking tin with baking paper, leaving handles above two sides. Pat the halved pitted cherries dry.
02 -
Mix flour, cocoa, brown sugar, baking powder and salt in a bowl. Rub in cold butter until clumps form, then stir in egg yolk and squeeze gently into a crumbly dough.
03 -
Press about two-thirds of the mixture firmly and evenly into the base of the tin. Bake for 12 minutes, then remove from the oven.
04 -
Toss cherries with caster sugar, cornstarch and lemon juice just before using. Scatter evenly over the warm base, including the thin coating of juice.
05 -
Crumble the remaining cocoa dough over the fruit, leaving small gaps. Bake another 25–28 minutes until the topping looks set and cherry juices bubble through some gaps.
06 -
Cool in the tin for at least 90 minutes before lifting out and cutting into 12 bars. The filling firms as it cools; cutting while hot will make the layers fall apart.
07 -
Keep covered in the refrigerator for up to four days. Let portions stand briefly before serving if you prefer a softer crumb.