Place washed unpeeled oranges in a medium saucepan. Cover with cold water and bring to the boil. Boil, covered, 30 minutes; drain. Repeat process with fresh water, boil about 1 hour or until oranges are tender; cool.

Preheat oven to 180°C. Grease a deep 22cm round cake pan and line base and side with baking paper.

Process the blanched almonds with 2 tbsp of the sugar until finely chopped.

Trim ends off oranges and discard. Halve oranges; remove and discard seeds. Process oranges, including rind, with baking powder until mixture is pulpy.

Beat eggs and remaining sugar in medium bowl with electric mixer about 3 minutes or until fluffy and paler in colour. Fold in almond mixture, ground almonds, flour and orange pulp. Pour mixture into pan. Bake about 1 hour. Cool cake in pan.

Turn cake, top-side up, onto serving plate; dust with sifted icing sugar.