For the crumble, which will be used as the cake’s topping, James put flour, butter, sugar, and ginger in a bowl and rubbed them together using his fingers.
He broke the mixture into chunky, crumbling pieces.
Next, he reached for a cake tin and laid some greaseproof paper on the bottom of it.
“Get into the habit of using paper like this,” James said.
The rhubarb was by now roasted, and he put the chopped pieces in the tin, before laying the cake mixture on top of them.
Next, the chef topped the mixture with the crumble.