1. Preheat the oven to 350 F. Thoroughly spray 3 6″ cake pans with nonstick spray and line the bottoms of the pan with parchment paper. Lightly flour the bottoms of the pan and set aside. 
2. In a large mixing bowl, sift together the flour, cocoa powder, baking soda, baking powder and salt. In the bowl of a stand mixer fitted with the paddle attachment, or using a handheld electric mixer, beat the softened butter on high for 1 minute. Add in the sugar and beat for another 2 minutes. With the mixer running on low, add the eggs, one at a time, scraping down the sides with a spatula. Add in the vanilla extract and beetroot powder and mix for another minute. 
3. With the mixer running on low, add in half of the sifted dry ingredients, followed by half of the buttermilk, then the remaining dry ingredients, the vinegar, then the last of the buttermilk. Mix just until combined. 
4. Divide the cake batter between the 3 prepared pans and place them in the oven for 26-27 minutes or until a toothpick inserted in the center of the pan(s) comes out clean. Let the cakes cool for 10 minutes before running a knife around the edges of the pan and inverting the cakes on to a wire rack to cool completely before frosting.
5. Prepare the whipped cream cheese frosting. In the bowl of a stand mixer fitted with the whisk attachment, whip the cold cream cheese for 1 minute on high until smooth. Add in the sugar and mix again for 1-2 minutes. 
6. With the mixer running on low, add in the vanilla, followed by cold whipping cream. Once you’ve added all the whipped cream, add in the salt, then turn the mixer to high and whip the mixture until stiff peaks form and the frosting is light and fluffy. Frost the cooled cake layers and serve!

Cake can be stored at room temperature, covered, for 1-2 days. Leftover cake can be stored in the fridge, in an airtight container, for 3-4 days, or in the freezer for up to 2 months. Unfrosted cake layers can be tightly wrapped in plastic wrap and placed in the freezer for up to 3 months.