Put the oven on gas mark 4 and fill a cupcake tray with cases.
Add the butter, sugar, flour and eggs in a mixing bowl and mix until fully incorporated then add your butterscotch powder along with the milk then mix until fully incorporated.
Fill the cupcake cases using an ice cream scoop and then put in the oven and bake for 20 minutes. Once cooked, take them out and transfer to a cooling rack and leave to cool.
Using a cupcake corer, core out the middle of each cupcake once they have cooled and fill the middle with the toffee sauce.
For the buttercream, beat the butter until it is pale and fluffy, then add in your icing sugar a bit at a time until it is all fully incorporated then add in the butterscotch powder and mix again until incorporated.
Fill a piping bag with the buttercream and pipe the icing on to the top of each cupcake then add some sprinkle or little bits of toffee.