Wash 2 large oranges and place in a medium saucepan filled ¾ full with water. Bring to a boil then reduce heat to low, cover and simmer for 90 to 120 minutes till the oranges are soft. Use a straining spoon to remove the oranges and set aside on a dish to cool.
Preheat the oven to 350℉/180℃/160℃ Fan
Slice the oranges in half to remove any pips. Purée the oranges (including the peel, pith and flesh) in a blender.
Separately, beat 6 medium eggs in a large bowl. To this, add 250 g ground almonds, 250 g sugar, 1 teaspoon baking powderthe orange purée and mix together well.
Grease a 9-inch springform pan with butter and dust lightly with 1 tablespoon ground almonds.
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 to cool in the tin before removing from the springform.
Glaze
In a small saucepan on medium heat, add ½ cup apricot jam and 1 tablespoon water. Stir till the jam melts and the becomes like a thick syrup, coating the back of a spoon. Remove from heat and cool till warm. Brush over cake then set aside to cool. Use a small sieve to dust 2 tablespoons confectioner's sugar over the top (optional) before serving.
Notes
Make ahead - This orange cake tastes even better the next day as the flavours develop.The glaze works beautifully with this cake.*To make it gluten free use a gluten free baking powder.To make it paleo use one and a half cups of a light honey with a mild flavour instead of sugar.Adding spice - If you wish to add spice, mix in 1 teaspoon cinnamon and ½ teaspoon ground cardamom when adding almond flour to the mixture.Fan assisted ovens, reduce the baking temperature by 50℉/20℃ degrees and you may need to reduce the cooking time. Check the cake in the last 20 minutes, by inserting a clean knife through the middle. If it comes out wet, check again after another 5-10 minutes. If it comes out only slightly sticky, it is done.Texture - this cake should have a cake-y exterior and pudding-like center.Store in an air-tight tin at room temperature for 4- 5 days or wrap individual slices and freeze for up to 6 months. Defrost overnight in the fridge or on the counter.