Wash 2 large oranges, place in a saucepan and fill till covered with water. Bring to a boil and simmer for 90 to 120 minutes, till oranges are soft, then transfer the oranges to a plate to cool.
Preheat the oven to 350℉/180℃/160℃ fan.
Slice the boiled oranges into quarters and remove any seeds, then puree both entire oranges (including the skin) in a blender and set aside.
In a large bowl lightly beat 6 medium eggs then add 250 grams ground almonds, 250 grams sugar, 1 teaspoon baking powder, orange purée and mix well.
Grease a 9-inch springform pan with butter and line with parchment paper so it hangs over the sides.
Pour the mixture into the springform pan and bake for 45-50 minutes, till the top is golden brown and a skewer comes out only slightly sticky.
Allow the cake to cook in the pan before removing.
Apricot glaze
Spread a thin layer of the 100 grams apricot jam over and round the sides of the cake.
Chocolate frosting
Grate 130 grams unsweetened dark chocolate and set aside.
In a small saucepan, add 250 ml double or heavy cream and 40 grams sugar and stir over low heat. Remove from the heat just before it starts to boil.
Stir in the chocolate till fully combined then set aside to cool.
Frost the cake and top with 1 tablespoon grated chocolate and 1 teaspoon orange zest (optional).
Notes
Helpful tips
Lightly grease the springform pan then line with parchment paper so the paper sticks to the sides of the pan.Bake till the top is golden brown and a skewer comes out only slightly sticky.Use a good quality 100% cacao, unsweetened dark chocolate which does not have any added flavours.To make the frosting grate the chocolate for quick and easy melting. Garnish with grated chocolate and orange zest (optional).
Make ahead and storing
The orange cake tastes even better when made ahead so the flavours have time to develop.The orange cake without frosting can be frozen. Wrap in kitchen paper and then plastic and freeze for up to 6 months. Defrost overnight in the fridge or on the counter.Store the cake with or without frosting in a closed container and keep at room temperature for 4-5 days.Do not store in the fridge as the cake will dry out and the chocolate will lose some of its flavour.Note: This cake tastes best eaten at room temperature.