Preheat the oven to 200 degrees Celsius (392 degrees Fahrenheit) (regular oven).
Melt the butter in a pot and then mix the sugar together with the butter.
Add buttermilk and stir it around.
Then add flour, cinnamon, and baking soda.
Stir everything together.
Pour the cinnamon batter into a greased baking tray. Mine is approximately 20 x 30 centimeters.
Place the baking tray in the preheated oven.
Let the cake bake for 30 minutes. You can check if the cake is done by inserting a knitting needle or a wooden BBQ skewer into the center of the cake.
Take the cake out of the oven and let it cool when it is fully baked.
Find a bowl and add all the ingredients for the icing.
Stir it well together until you get a smooth mixture.
Spread the icing on the cake once it has cooled.
Serve.