Preheat the oven to 180 C / Gas 4. Grease and flour a 23cm or 25cm spring form cake tin.
Place egg yolks, softened butter and sugar in a large bowl; use an electric beater to mix until smooth.
In another bowl, sift the flour and baking powder together. Set aside.
Place egg whites and pinch of salt in a perfectly clean and dry bowl. Use an electric mixer with clean dry beaters to beat egg whites until stiff peaks form. Set aside.
Stir orange zest into butter and sugar mixture. Add flour, a little at a time, alternating with egg whites, until everything is combined. Stir in milk and pour the cake mixture into the prepared cake tin.
Bake in the preheated oven for 35 - 40 minutes, or until a skewer inserted in the centre of the cake comes out clean.
Unlock spring form tin and transfer cake to a wire rack to cool slightly.
Transfer the cake onto a serving plate; prick the top of the cake all over with a skewer. Pour over orange juice mixed with sugar. Let stand for 1 hour before serving, so the cake has the time to soak in the juice.
For a simple but impressive decoration, place some orange or tangerine segments in a circle on top of the cake.
Once cold, cover with cling film and refrigerate until it's time to serve. Remove from the fridge about 10 to 15 minutes before serving.