Preheat the oven to 180C/350F and line a 12 hole cupcake tray.
Place the butter and sugar into a large bowl or the bowl of your stand mixer and beat until light and fluffy, about 2 minutes on med-high speed.
Add in the oil, eggs and vanilla extract and mix until well incorporated, about 1 minute on med-high speed.
Add in the flour, cocoa powder, baking powder and milk and mix until well incorporated, light and smooth, about 1 minute on med-high speed.
Divide the batter between the cupcake liners, 3/4 full.
Place the cupcakes in the oven for 20-25 minutes, until risen, they spring back and an inserted skewer into the centre comes out clean.
Remove from tin immediately and place on wire rack to cool completely.**
Once cooled, make the frosting, place the butter and icing sugar into a large bowl or the bowl of your stand mixer and beat until light and fluffy, 2-3 minutes on med-high speed.
Add in the vanilla, melted chocolate and pinch of salt and beat until light and fluffy, about 1 minute on med-high speed.
Either spoon the frosting onto the cupcakes, or half fill a piping bag and pipe a swirl on each cupcake.
Cupcakes will keep in an airtight container, in the fridge, for 3 days.