Gluten Free Banana Nut Sponge

What to do with a too ripe banana?   In my collection of recipes written out from borrowed library books I found a Banana Sponge recipe that I thought I could adapt to make  gluten free.  It worked a treat!  It's a delicious, moist and tasty sponge.  The original recipe was served with mango cream.  I had some frozen raspberries, some low fat cream cheese and yoghurt and used them instead to make a scrumptious filling.  I dont know the name of the book I got the original recipe from, except that it was a healthy heart cookbook. Anyway here is my adapted recipe:

1 cup ground almonds (could use  hazelnuts)
1/2 cup rice flour
1/4 cup buckwheat flour
1 ripe banana
1 teaspoon lemon juice
3 egg yolks
4 egg whites
2/3 cup of sugar

Preheat oven to 175 deg C.  Lightly spray cake tin (i used a silicon ring pan with fancy bottom - has a special name that I cant remember.)
Place the ground almonds on a baking tray lined with baking paper and toast in the oven until lightly browned - about four minutes. I used four bowls. In the first I mixed  the toasted nuts and the flours together.
In the second bowl I mashed  the banana,  and then added the lemon juice to this and mixed until it was a smooth paste.
In the third bowl, beat the egg yolks and 1/4 c of the sugar until pale and thick. Add the banana and lemon juice mixture ( in the second bowl) to this.
In the fourth bowl beat the egg whites until soft peaks form, then add the unused sugar and beat until it is dissolved.  Then add the egg yolk and banana mixture to the egg white mixture and stir until just combined.  Then carefully fold in the flour/nut mixture.
Spoon into prepared pan and bake for 25-30 minutes or until cake springs back when lightly pressed (and skewer inserted comes out clean)
Allow to cool in pan for 10 minutes before turning out on to wire rack.  When cool cut through the centre and fill with raspberry creme (if desired) - the cake is quite yummy with out any filling.

Raspberry filling
1 cup raspberries (frozen, thawed are fine)
1/2 cup light cream cheese
1/2 cup yoghurt (I used no added sugar raspberry flavoured)
2 teaspoons stevia (or sweetening to taste)

Blend all the above ingredients.  If too stiff add more yoghurt. If too runny add more cream cheese.