Preheat your oven to 180°C (350°F) and grease and line a rectangular baking tray with parchment paper.
In a large mixing bowl, cream together the softened butter and Tate & Lyle Caster Sugar until light and fluffy.
Add the eggs, one at a time, beating well after each addition. If the mixture starts to curdle, add a tablespoon of flour and continue mixing.
Sift the self-raising flour into the bowl and fold it gently into the mixture. Add the orange zest and orange juice, and mix until well combined.
Divide the mixture into two equal parts. Leave one part plain, and sift the cocoa powder into the other part. Mix until the cocoa powder is fully incorporated.
Spoon alternate dollops of the plain and chocolate batters into the prepared baking tray, creating a marbled effect.
Sprinkle the chopped dark, milk, and white chocolates evenly over the top of the cake mixture.
Bake in the preheated oven for 25-30 minutes, or until a skewer inserted into the center comes out clean.
While the tray bake is baking, prepare the chocolate orange drizzle. Melt the dark chocolate in a heatproof bowl set over a pan of simmering water. Stir in the orange zest.
Once the tray bake is baked, remove it from the oven and allow it to cool in the tray for a few minutes. Then, transfer it to a wire rack to cool completely.
Once the tray bake is completely cooled, drizzle the melted chocolate orange mixture over the top using a spoon or a piping bag.
Finally, sprinkle the remaining orange zest over add a segment of chocolate orange evenly spaced (we find 12 evenly space where you will slice works best). Cut into squares and serve. Enjoy your delicious Chocolate Orange Tray Bake!