1.Place unpeeled orange in medium saucepan. Cover with cold water, bring to boil. Boil, covered for 50-60 minutes, until tender. Drain. Cool.
2.Preheat oven to 180°C. Lightly grease an 18 x 28cm slice pan. Line base and sides with baking paper, extending paper 2cm above pan edge.
3.Place toasted almonds and 2 tablespoons of sugar into a food processor or blender. Process until finely chopped.
4.Trim ends from orange and discard. Halve orange. Remove and discard seeds. Place orange with rind, baking powder and cinnamon into a food processor. Process until mixture is pulpy.
5.In a small bowl, using an electric mixer, beat eggs, remaining sugar and vanilla for about 3-4 minutes until mixture is light and fluffy. Fold in almond mixture, combined meal and flour, and orange pulp. Pour mixture into prepared pan, smoothing top.
6.Bake for 35-40 minutes until slice is cooked when tested. Cool in pan. Serve in squares, dusted with icing sugar.
This cake freezes well. Store in an airtight container for up to three days. Toast almonds by tossing in a dry frying pan over a medium heat until golden. Remove from pan immediately to prevent burning.Note