Thoroughly wash the oranges. Place them in a pot, cover with cold water, and then remove the oranges. Bring the water to a boil, add the oranges back in, reduce to a simmer, and cover with a plate to keep the oranges submerged. Cover the pot and let it simmer for two hours.

While the oranges are simmering, lightly butter a 9 or 10-inch springform pan. Cut a circle of parchment paper to line the bottom and butter that as well.

Preheat your oven to 350°F (175°C).

Once the oranges are done simmering, take them out of the water and let them cool enough to handle. Cut them open and remove the seeds.

Place the orange flesh into a food processor and blend it into a puree, adding no more than 6 tablespoons of the cooking water if needed.

In an electric mixer, beat the eggs and sugar using the whisk attachment until the mixture is pale, fluffy, and thick.

Gently fold in the ground almonds, baking powder, salt, and the orange puree to create a thick batter.

Pour the batter into the prepared cake pan and bake for 45 to 60 minutes, or until the cake is firm in the center and a cake tester comes out mostly clean.

Allow the cake to cool completely in the pan. Once cooled, run a knife around the edge and carefully remove the sides of the pan.

Invert the cake onto a plate, remove the bottom of the pan, and then flip it back onto a stand. Dust the top with powdered sugar and proudly announce, 'THIS CAKE HAS FOUR ORANGES IN IT!'