Hi Merlin
I don't have the GF book but have found a recipe for GF Coconut and dulce de leche cake on the [http://recetario.es/recetas/tarta-de-coco-y-dulce-de-leche/25562]Spanish Thermomix website[/url]. If it looks like what you are after, here it is in English:
The Cake
150 g sugar
250 g pastry flour without gluten
50 g grated coconut
100 g butter (room temperature)
2 eggs
100 g coconut milk or 1 coconut yoghurt
1 pinch salt
Decoration
Dulce de leche with cream
20 g grated coconut
Preheat oven to 180º
Put all the ingredients for the cake into the bowl and set 20 seconds / speed 6.
Pour into a greased tin and bake for 25 to 30 minutes.
Unmould the cake and leave to cool completely.
Cut the cake into two layers and cover the bottom half with dulce de leche.
Put the other half of the cake on top and cover with dulce de leche.
Sprinkle with coconut.
JB