You probable have seen as well all of this great striped cakes and thought about how to get this great effect. In addition you want this super smooth cake with a sharp edge. It is really simple and I made a step by step tutorial for you how to get buttercream stripes on a cake.
Prepare some buttercream and seperate two portions (3/4 of it and 1/4). I used 400ml sweetened condensmilk and 250g unsalted butter for it, but you can also use an american buttercream with just butter and powdered sugar. Dye both portions in your two prefered colors.
To get a cake with sharp edge you can use this tutorial to stack the cake. You can use whatevery cake and whatever filling you like. The filling should not be to smooth and thick as you need to turn around the cake later on in the process. To get a striped buttercream cake and still get the sharp edge, frost the cake with one color of buttercream (the one where you have the bigger portion). The buttercream neads to stick out some over the cakeboard to be able to scrap something off later. Now chill the cake for some minutes.
To get the striped effect you need a toothed trowel, which you can get out of the baking island but is also used for laying tials. I bought one which has a toothed and a flat side to be able to create the stripes and crape of the excess icing later.
The next step is to create the grooves with the trowel. It is important the grooves are deeper as the cakeboard, but there needs to be still material sticking out around the cakeboard to be able to scrape something off later and flatten the cake. The easiest is to scrap right along the bottom plate and stick the teeth about half of their size into the buttercream. Move it all along the cake till you have grooves all around. If you don't got the grooves deep enough you don't have to worry, just rework them with the other end of a spoon.
Now fill the second color of buttercream into a pipingbag with a round piping tip and fill up the the grooves all around the cake.
Don't worry if the surface is not smooth, because this comes in the next step.
Now chill the cake again a few minutes bevore you do the last step. You scrape the excess frosting off all around the cake. You can do it exactly like in this description. After you scraped off the excess, changed the cakeboard and turned the cake you can easily lift the plate off and get rid of the paper which you put on the bottom in the beginning (if you did not forget it like myself in this pictures). Now you should have a striped buttercream cake which you just need to decorate how you like. I used a piping tip Wilton 32 and a few sugar pearls.