Instructions:
- Preheat the oven to 350°F (180°C). Grease and flour a 9-inch (23 cm) round cake pan.
- In a large bowl, cream together the butter and white sugar until light and fluffy. Beat in the egg yolks, one at a time, until fully incorporated.
- In a separate bowl, whisk the egg whites with the cream of tartar until stiff peaks form.
- In another bowl, sift together the cake flour, baking powder, and salt.
- Gradually add the flour mixture to the butter mixture, alternating with the fresh orange juice, until just combined.
- Fold in the egg whites, then gently fold in the orange zest.
- Pour the batter into the prepared cake pan and smooth the top with a spatula.
- Bake in the preheated oven for 35 to 40 minutes, or until a toothpick inserted into the center of the cake comes out clean.
- Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
- Sprinkle the confectioners’ sugar over the top of the cake just before serving.
