Method

• Preheat oven to 180C /160C fan assisted, with rack in one level lower than centre
• Lightly grease 18cm square cake tin with cooking spray or butter, and line with greaseproof paper, leaving an overhang on 2 sides (this acts as a handle)
• Stir together rhubarb - trimmed and cut (on the angle) into ½ cm thick slices, and half cup sugar; set aside to macerate
• Whisk together flour and baking powder
• Beat together butter, remaining cup sugar, and the orange zest until light and fluffy
• Beat in eggs, 1 at a time, then beat in vanilla
• Beat in flour mixture in 2 additions, alternating with sour cream, beginning and ending with flour mixture
• Make the crumb topping: Stir together flour, ginger, brown sugar, add melted butter; stir to combine
• Pour mixture into prepared tin
• Top with rhubarb mixture, and sprinkle with crumb topping
• Bake until golden on top and cooked through, about 45 minutes, check the cake however as it can take a little less time or sometimes a little more
• Let cool completely in tin on wire rack, then lift cake from pan using greaseproof paper
• Remove greaseproof paper before serving, cut buckle into 4cm squares