Stack alternate layers of cake and frosting, spoon it on or pipe it depending on what you have to hand.
Use a set square or kitchen knife to keep them straight as you stack.
Then pop it in the fridge while you make the coloured buttercream.
Give each cake a small shake back-and-forth to get it to settle onto the frosting.
Use some vanilla buttercream and add some food colouring to get your desired shade.
Remember, the colour of your buttercream will be paler until it has rested overnight, so the shade will get slightly more intense/darker.
I started with a liliac food colouring and added in some pink to make the shade more intense.
Once it is coloured, cover with clingfilm to stop it crusting, and keep at room temperature.
Put a nice big dollop of the coloured buttercream onto your cake then, using a table knife or spatula, spread it all over the cake. Take your time and make sure there are no air pockets between the cake layers.
This coat doesn’t have to be neat as you are just using it to stop any crumbs or smears of the buttercream from the interior of the cake getting in your final layer.
Refrigerate the cake for an hour.
Once your cake is chilled and stable, use the knife or a spatula to add more buttercream. I prefer to use a piping bag to help me get the frosting on the cake mess free, but if you don't have a piping bag, just try and apply the dollops of buttercream evenly around the edges.
Use a container to keep your bags open whilst you fill; with piping bags I use a plastic bottle which has been cut in half.
Use the set square or knife to scrape the sides until the coating is even. If you have lots of air holes (like me); refrigerate, add a third coat, and smooth again.
Put the ball of buttercream on top of the cake.
Slowly drizzle on the icing, (cut the corner of the sandwich bag and pour) taking care to cover the top.
Once the top is covered start a few drips on the edge, if they haven't started already.
My icing could actually have been a little thicker as it ran more than I was wanting!