Wash the oranges thoroughly. Place them whole (unpeeled) in a large pot and cover with water. Bring to a boil, then simmer for 1 to 1.5 hours until very soft. Drain and let cool completely.

Preheat your oven to 375°F (190°C). Grease a 9-inch springform pan and line the bottom with parchment paper.

Cut the cooled oranges into quarters, remove any seeds, and place the chunks (peel and all) into a food processor. Blitz until you have a smooth orange purée.

In a large bowl, beat the eggs and sugar until pale and slightly thickened.

Add the almond flour, baking powder, ground cardamom, and the prepared orange purée to the egg mixture. Gently mix until well combined.

Pour the batter into the prepared tin and bake for 45 to 60 minutes. Check by inserting a skewer; if it comes out clean (or with just a few moist crumbs), it is ready. If the top browns too quickly, cover loosely with foil.

While the cake bakes, prepare the syrup. Combine honey, water, and lemon juice in a small saucepan over medium heat. Simmer for 3-5 minutes until slightly thickened.

Remove the cake from the oven. While the cake is still warm, prick it all over with a skewer and slowly pour the warm honey syrup over the top.

Allow the cake to cool completely in the tin before removing. Garnish with sliced almonds if desired.