Pre-heat your oven to 180°C (350°F) and place your oven shelf in the centre. Grease and line with parchment paper, a 2 lb 23 x 14cm (9 x 5.5-inch) loaf pan.
In a separate bowl sift the flour, cocoa powder, baking powder and salt.
Add the butter, caster and brown sugar and orange zest into the bowl of your electric mixer, fitted with the paddle attachment (or using your handheld electric whisk) and beat until smooth and creamy, about five minutes.
Beat in the eggs, one at a time, mixing until combined between each addition. Then add the vanilla bean paste and orange juice and mix to combine. Ensure that you scrape down the sides of the bowl. Add the dry ingredients into the mixture gradually and beat until just combined.
Pour cake batter into the greased loaf tin and bake for 60 to 70 minutes or until a skewer comes out clean. Leave the cake in the tin for ten minutes and then run a knife around the edge before turning out onto the wire rack to cool completely.
Cream cheese frosting
In the bowl of an electric stand mixer fitted with a paddle attachment, beat the cream cheese, butter and vanilla bean extract on medium-high until completely smooth. Reduce the speed to low and gradually add the sifted icing sugar. Then beat on high speed for 1 minute. If the frosting is too runny then add more icing sugar, 2 heaped tablespoons at a time.
Once the cake has completely cooled, spread the frosting over the cake and decorate with orange zest. Slice and serve.
To store: This cake can be stored in the fridge in an air-tight container for up to 3 days. Allow to come to room temperature before eating.