Cake au beurre fourré

wheat flour 50.0% , custard filling 20.0% , sugar 15.0% , water 7.5% , vegetable oil 3.8% , Stabiliser 1.9% , skimmed milk powder 0.9% , lactose 0.5% , glucose syrup 0.2% , modified potato starch 0.1% , free-range protein powder 0.1% , Thickener 0.0% , Preservative 0.0% , milk proteins 0.0% , flavouring 0.0% , Colour 0.0% , sugar 0.0% , butter 14.0% , free range eggs 0.0% , water 0.0% , potato starch 0.0% , Raising agent 0.0% , Stabiliser 0.0% , Emulsifier 0.0% , glucose-fructose syrup 0.0% , salt 0.0% , Preservative 0.0% , rice flour 0.0% , soya flour 0.0% , Thickener 0.0% , milk proteins 0.0% , vegetable oil 0.0% , Antioxidant 0.0% , Colour 0.0%