In a saucepan, heat the orange juice just until it’s about to boil (but don’t let it boil).
Remove from heat and add the chocolate and butter. Let them melt together and stir until smooth. Set aside.
In a separate bowl, beat the eggs and add the cream.
Grate the orange zest and add it to the egg and cream mixture.
In a large mixing bowl, combine the flour, baking powder (if using), and brown sugar. Mix well.
Add the chocolate mixture to the dry ingredients. Mix thoroughly until you have a smooth, uniform batter – this may take a bit of effort.
Add the egg mixture and stir until fully combined. The batter should be creamy and rich.
Preheat the oven to 180°C (356°F), top and bottom heat.
Grease a cake pan with butter and pour in the batter. Tap the pan gently on the countertop to remove any air bubbles.
Bake for approximately 35 minutes, or until a toothpick inserted comes out clean.
Let it cool on a wire rack, then remove from the pan.