The day before, soak the raisins in 100ml rum and allow them to sit and steep overnight.
Preheat oven to 180 C.
Grease a 24cm bundt tin with butter and then tap out with flour.
Make the filling first; mix together the cream cheese, egg, icing sugar, flour and vanilla until smooth and then put into a piping bag. Set aside until needed.
In a stand mixer, beat together the butter and sugar until light and fluffy. Add the eggs one at a time, beating between each, until incorporated. Finally, add the oil and vanilla and beat again.
In a bowl mix together the flour, baking powder, bicarbonate of soda and salt. Add this into the egg and butter mixture bit by bit, alternating with the milk. Take care not to overmix. Finally add the soaked raisins (they should have soaked up all the rum by now) and orange zest and fold through the mixture.
Place just over half of the mixture into the prepared tin and using a spoon smooth the mixture to fill the tin. When the mixture is evenly distributed, place the spoon into the middle of the mixture and drag it around the whole mixture - forming a well in the cake batter. Snip the end off the piping bag containing the filling and pipe the filling into the well you have created - you want to make sure the mixture stays in the middle of the cake and doesn’t touch the outside, so be careful when piping. When the filling is in place, spoon dollops of the remaining batter to cover it and smooth gently with a spoon to cover.
Bake in the oven for 50 minutes - 1 hour until golden brown and and cooked through. If the bundt looks like it’s browning too quickly, cover with tin foil and put back into the oven.
Whilst the cake is cooking, make the rum caramel sauce.
In a saucepan add the granulated sugar and water and slowly heat, gently stirring to help dissolve the sugar. Use a pastry brush to brush down the sides of the pan with water to avoid crystallisation. Continue to heat the sugar until all of it dissolves and then allow the caramel to bubble until it turns a medium deep amber colour.
Once it has reached this stage, take the pan off the heat and add the cream and rum together. Allow the mixture to bubble and stir continuously. Pour the caramel into a bowl and allow to cool and thicken.
Once the cake has been removed from the oven, allow to cool for at least 30 minutes before turning it out from it’s tin, and allow to cool completely before drizzling over the rum caramel sauce.