1 tsp. vegetable oil, plus extra to grease
6 gelatine leaves
350 g (12oz) good quality no-peel Seville orange marmalade, plus extra to stick
125 g (4oz) dark chocolate, broken into pieces
5 mini Jaffa Cakes, halved
FOR THE CAKE
150 g (5oz) self-raising flour
150 g (5oz) caster sugar
150 g (5oz) unsalted butter, very soft
3 medium eggs
2 tsp. vanilla extract
2 tbsp. milk
Grease a 900g (2lb) loaf tin with oil and carefully line with oiled clingfilm. Put gelatine leaves to soak in a small bowl of cold water for 5min.
Gently heat marmalade in a small pan, whisking frequently until melted and smooth. Lift gelatine out of bowl and squeeze out excess water. Add soaked gelatine leaves to marmalade and whisk again over a low heat until gelatine is melted and combined. Tip marmalade mixture into prepared tin and leave to cool to room temperature. Freeze for 45min until set firm.
Remove tin from freezer and gently lift out jelly using clingfilm. Fold edges of clingfilm over top to wrap it and set aside at room temperature.
Line same loaf tin with baking parchment. Preheat oven to 180°C (160°C fan) mark 4.
Put all the cake ingredients in a large bowl, then use an electric handwhisk to beat them together until just combined and smooth (about 30sec). Tip mixture into prepared tin, smooth to level and bake for 45-50min, or until risen, golden and a skewer inserted into centre comes out clean. Allow to cool in tin completely.
Remove cake from tin, peel off parchment and level-off domed top with a serrated knife. Invert cake on to a board or serving plate so the bottom of the cake becomes the top.
Spread a little marmalade all over top of cake. Carefully unwrap jelly and use clingfilm to help you flip it on to the top of the cake. Press down gently to stick. Trim off any overhang with a sharp knife.
Put chocolate in a heatproof bowl set over a pan of gently simmering water, stirring occasionally until melted and smooth (don’t let the bottom of the bowl come in contact with the water). Remove from heat and stir oil in really well. Leave to cool for 5-10min, until chocolate is room temperature and no longer feels warm when you spoon a drop on your finger.
Carefully pour cooled melted chocolate on top of jelly and spread gently, allowing a little chocolate to run down sides and cover the jelly (for the smoothest finish, try to resist going over chocolate again after you’ve spread it once, as it can set quickly). Quickly decorate top with halved Jaffa Cakes, then allow chocolate to set before slicing and serving.