Melted butter, to grease
2½ cups gluten-free plain flour
2 tsp xanthan gum
1¼ tsp gluten-free baking powder
½ cup caster sugar
Finely grated zest and juice of 1 large orange
125g butter, chopped, chilled
1 tsp vanilla extract
Extra 125g butter
½ cup brown sugar
2 cups sultanas
1 Tbsp gluten-free cornflour
½ tsp ground cinnamon
Preheat oven to 160°C. Grease a 30 x 20cm lamington tin with melted butter and line with baking paper. Put flour, xanthan gum, baking powder, sugar and ½ of the orange zest in the bowl of a food processor and pulse until combined. Add butter and process until mixture resembles fine breadcrumbs. Add egg, vanilla and 2 Tbsp of the orange juice, then process until a dough forms. Divide dough in half. Form 1 half into a log, then enclose in plastic wrap and refrigerate until required. Press remaining half of dough evenly over base of prepared tin.
Combine extra butter, brown sugar, sultanas, cornflour, cinnamon, remaining orange zest and 2 Tbsp of the juice in a medium saucepan. Stir over a medium heat until butter and sugar has melted and mixture comes to the boil. Simmer for 2 minutes. Set aside to cool.
Spread sultana mixture over dough in base of tin. Coarsely grate chilled dough and sprinkle over sultana mixture. Bake for 25 minutes or until golden and firm to the touch. Cool in pan, then cut into pieces and serve.
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