Place the whole unpeeled oranges in a large pot and cover with water; bring to a boil and simmer for 1 hour until soft (ensure they stay submerged).

Drain the oranges and let them cool slightly, then cut them into quarters, remove any seeds, and pulse in a food processor until smooth.

Preheat your oven to 375°F (190°C) and grease a 9-inch springform cake pan with oil or butter.

In a large mixing bowl, beat the eggs and 1 cup of granulated sugar together until pale and frothy.

Gently fold in the almond flour, baking powder, ground cardamom, and the prepared orange purée until well combined.

Pour the batter into the prepared pan and bake for 45 to 50 minutes, or until a skewer inserted into the center comes out clean and the top is golden brown.

While the cake bakes, make the syrup by combining the orange juice, 1/3 cup sugar, and crushed cardamom pods in a small saucepan.

Simmer the syrup over medium heat for 5 minutes until the sugar dissolves and the liquid thickens slightly, then remove from heat.

Once the cake is removed from the oven, immediately poke holes all over the surface with a skewer and pour the warm syrup evenly over the top.

Allow the cake to cool completely in the pan to absorb the liquid before garnishing with sliced almonds or pistachios and serving.