Preheat oven to 170 C / Gas 3. Grease a 26cm round springform tin with cooking oil spray and dust with rice flour.
In a large bowl, beat egg yolks with 125g sugar until thick and pale using an electric mixer. This will take about 5 minutes. Stir in the rice flour and orange juice, then fold in the ground almonds and cinnamon.
In a separate glass or metal bowl, beat 3 egg whites until they can hold a stiff peak. Fold into the almond mixture until well blended. Pour into the prepared tin and spread evenly.
Bake for 35 to 40 minutes in the preheated oven, until a skewer inserted into the centre comes out clean. Cool in the tin on a wire rack. Run a knife around the outer edge of the cake to help remove it from the tin.
Whilst the cake is cooling, make the orange sauce. Cream together the butter and 400g sugar in a medium bowl. Stir in the cream and place the dish over a pan of barely simmering water. Stir in orange juice and zest. Beat 4 egg whites in a separate bowl until soft peaks form. Fold into the orange sauce. Spoon over the cake and serve immediately.