Preheat the oven to 180°C (356°F). Grease a jumbo muffin pan or mini cheesecake pan.
In a large mixing bowl, combine the caster sugar and orange zest. Use your fingers to rub the zest into the sugar, releasing the citrus oils for enhanced flavor.
Add the eggs and bourbon vanilla paste, then whisk using an electric mixer for 4-5 minutes until the mixture becomes light and fluffy.
Mix in the soft butter until smooth and fully incorporated.
Incorporate the orange juice, mixing until well combined.
Sift together the flour, baking powder, baking soda, and salt, then gently fold into the wet ingredients until no lumps remain, ensuring a smooth batter.
Pour the batter into the prepared cake pan, spreading it evenly.
Bake for 35-40 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Cool the cake in the pan for 15-20 minutes before transferring to a wire rack.
Slice and enjoy the perfect balance of citrusy sweetness and tender crumb!
