Preheat the oven to 175°C.
Grease and line the bottom of a 21-22 cm, round cake pan with parchment paper. Scatter some sugar over it.
Zest the oranges and cut on of them into thin wheels. Arrange these tightly in a single layer on top of the parchment paper. Cut the other one into small chunks (or process in a small food processor).
In a large bowl, cream together the butter and sugar for about 5 minutes, using an electric mixer. Beat in eggs, one a time, mixing for 30 seconds after each addition.
Add the vanilla extract, mix, the add the almond meal, orange zest and pulp, together with any juices and mix on a low speed until combined.
In another bowl, mix the flour and baking powder, then add this to the wet ingredients. Gently mix until combined.
Tip the batter over the oranges, spreading out evenly and carefully.
Bake the cake for 30 to 35 minutes, until it is golden and a toothpick inserted in the centre comes out clean.
Cool the cake in the pan for about 10 minutes, then run a knife along the pan’s edges to loosen it. Transfer the cake onto a platter and cool completely. Turn it over and carefully remove the parchment paper. Dust with icing sugar just before serving.