Preheat oven to 160°C (140°C fan-forced). Lightly grease a deep 22cm square cake tin and line with baking paper.
Place whole oranges in medium saucepan and submerge in water. Place saucepan over a medium heat, cover and bring to the boil. Reduce heat to a simmer and cook for 1 hour. Remove from heat, drain and allow oranges to cool completely.
Pour boiling water into a small saucepan, about a third full and sit a small bowl on top. Add Haigh’s 70% dark chocolate pastilles and stir occasionally, until chocolate melts. Remove from heat and allow to cool slightly.
Place cooled oranges in a food processor and pulse to a puree.
Using an electric mixer, beat butter and sugar for 5 minutes or until light and fluffy. Add eggs one at a time, beating until combined. Add orange puree, almond meal, flour, cocoa and baking powder, stirring until combined. Add melted chocolate, stir to combine.
Pour mixture into prepared cake tin and bake in preheated oven for 1 ¼ hours or until a skewer comes out of the centre clean. Remove from oven, allow to cool in tin for 15 minutes, before turning onto a wire rack to cool.
Meanwhile, for the orange syrup, place sugar, juice and zest together in a small saucepan over a low heat, stirring until sugar dissolves. Bring to the boil and cook for 5 minutes.
Serve cake warm, drizzled with orange syrup and for a dessert option top with vanilla ice cream.