• Place the zested oranges (without their zest) in a large saucepan and cover with water until submerged. Place on medium heat and boil for 2-2.5 hours or until oranges are very tender when poked.
• Cool slightly and cut each orange in half so you can remove the pips. Blend the oranges until they turn into a pulp (you could also use the large side of a box grater to do this). Fold in the orange zest, and set aside.
• In a separate bowl, whisk the baking powder thoroughly with the almond flour. Set aside.
• In the bowl of a mixer, add the caster sugar and eggs and whisk on medium speed for 2-3 minutes until light and foamy.
• Add the orange mixture to the egg and sugar mixture and fold gently to combine. Add the almond flour mix to this, and fold to combine.
• Pour into a prepared 9x13 baking pan. Sprinkle with flaked almonds if using, and bake for 30-35 minutes or until a toothpick comes out clean. Cool completely.

For the glaze:

• In a sauté pan over medium heat, add the marmalade and the water. Stir until marmalade has melted and let it simmer for a minute or so. That's the glaze! Brush glaze onto cooled cake.