Place the softened butter and half of the sugar into the bowl of a stand mixer. Beat on high with the paddle attachment until light and airy.
Add the softened cream cheese, vanilla extract and salt and continue to beat until smooth and creamy.
Add the rest of the sugar and continue beating until light, airy, and smooth.
Place a spoonful of the frosting onto the center of your cake plate or serving platter. Turn one of the cinnamon roll cake layers out, placing it bottom-side down onto the center of the serving platter.
Smooth a thick layer of buttercream over the top of the first cake layer. Turn the second cake layer out of the pan and place it bottom side up so you have a nice flat surface on top. Gently press the layer down to make sure the top is flat and even.
Cover the cake in a thin layer of the frosting. If the cake is moving around too much you can place it in the fridge to help it set up a bit before frosting the outer edges.
Once the cake is frosted, gently scrape the sides with an offset spatula or the dull side of a knife to achieve a "naked cake" effect.
Place any leftover frosting into a piping bag fitted with a large star tip.
Pipe swirls of the buttercream alternating between tall and short swirls all along the top edge of the cake. Place one of the mini cinnamon rolls onto each of the short buttercream swirls.
Sprinkle the top of the cake with a little cinnamon, for an extra special look, try using freshly grated cinnamon sticks.
Set in the fridge for at least 2 hours to allow the frosting to set up.
Serve and enjoy!