1Preheat the oven to 180C/ 160C Fan/Gas 4. Grease the inside of a 2L domed metal mixing bowl. Cut a 20cm circle of greaseproof paper, snip cuts into it like the spokes of a wheel, far enough in so the paper overlaps and sits snugly in the bowl. Use to line the base of the bowl.
2Microwave the golden syrup for 3-5 secs until runny. In a separate bowl, beat together the oil, milk and eggs. In a third bowl, sift together the flour, cocoa and baking powder and stir in the sugar. Add the syrup and the milk mixture to the dry ingredients and beat into a thick batter. Pour into the lined metal bowl and bake for 1 hr 15 mins or until risen and a skewer inserted into the centre comes out clean. Cool completely on a wire rack.
3To make the buttercream, gently heat the sugar with 3tbsp water in a pan until it dissolves. Boil until it reaches 110C on a sugar thermometer.
4Beat the egg yolks with an electric hand-whisk while slowly pouring in the sugar syrup until thick, pale and mousse-like. Whisk in the butter, 1 cube at a time, then add the vanilla extract. Whisk until glossy and fluffy.
5Slice the cake into 3 horizontal layers and sandwich together with half the buttercream. Thinly spread half the remaining buttercream over the cake, smoothing well. Chill in the fridge for 30 mins until set. Spread the remaining buttercream over the cake, smoothing well again. Chill for another 30 mins. Using a small spatula, smooth the icing one last time. Chill until ready to glaze.
6To make the mirror glaze, soak the gelatine in 80ml cold water for 5 mins. Heat the sugar, glucose and 100ml water gently in a pan until the sugar dissolves. Bring to the boil until it reaches 103C. Remove from the heat. Add the soaked gelatine and stir until smooth. Stir in the condensed milk.
7Put the white chocolate into a bowl. Pour over the warm condensed milk mixture and leave for 5 mins. Stir until smooth. Test the mixture with a sugar thermometer – when it cools to 30C it is ready to use. Stir occasionally as it cools to prevent a skin forming.
8For a perfect finish, the glaze has to flow over the cake and drip off the bottom edge. For this, stand the cake on a plate smaller than its base, balance this on a small bowl, then put on a clingfilm-lined baking sheet.
9Divide the glaze between three bowls. Stir gel food colour into each to make three different shades. Pour over the cake, alternating colours so they form flowing patterns and cover the buttercream. Any excess will drip off the base. Leave to set for 25 mins.
10Lay the stars on baking paper. Once the glaze is set, arrange the stars on the cake. Transfer to a cake stand to serve.