Line a 20cm cake tin base with paper and preheat oven to 180°C.
Melt butter in a pan and mix with sugar, oil, cocoa, and vanilla.
Whisk in eggs, milk, and cream until smooth.
Sift in flour and baking powder, beat well, and pour into the tin.
Cover tin with foil and bake for 30 minutes.
Remove foil and bake for 20 more minutes until a skewer comes out clean.
Cool the cake completely on a wire rack.
Mix cocoa, icing sugar, melted butter, and cream to make the frosting.
Halve the cake horizontally and spread the bottom with whipped cream and jam.
Frost the top half, swirl with a spoon, and place on the bottom half.