Preheat the oven to 180°C (350°F), and line the sides and bottom of a 9-inch (23cm) spring-form cake tin with baking paper.
Juice and zest the oranges.
In a large mixing bowl, mix the almond meal, caster sugar, and baking powder. Make a well in the centre of the bowl and add the eggs, orange juice, and orange zest. Stir to combine into a wet batter.
Pour the batter into the prepared cake tin. Dust with the brown sugar, this will form a firm and chewy crust on top of the cake.
Carefully place the tin in the oven, and bake for 45 minutes or until a skewer inserted into the cake comes out clean. Remove from oven and serve warm. You can also top it with icing sugar to make it even more classically Spanish!