Prepare the Oranges: Place the whole oranges (unpeeled) in a large pot of water and bring to a boil. Simmer the oranges for 1 hour, adding more water if necessary to keep them covered. Drain the oranges and let them cool. Once cool, cut them into quarters, remove any seeds, and blend them (peels included) into a smooth puree.

Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a muffin tin or mini cake molds to prevent sticking.

Make the Batter: In a large bowl, beat the eggs and caster sugar together until pale and thick, about 3 minutes. Add the orange puree, almond meal, baking powder, and vanilla extract to the egg mixture. Gently fold until the ingredients are well combined, ensuring a smooth, even batter.

Bake the Cakes: Pour the batter into the prepared muffin tin or mini cake molds, filling each mold about three-quarters full. Bake for 45-50 minutes or until a skewer inserted into the center of a cake comes out clean and the tops are golden.

Cool and Serve: Let the cakes cool in the tin for 10 minutes, then transfer them to a wire rack to cool completely. Dust with powdered sugar before serving, if desired.