Preheat oven to 350ºF (180ºC). Whisk together flour, cocoa powder, baking powder, baking soda and salt; set aside. In measuring cup, whisk together buttermilk, food colouring and vinegar; set aside.
In separate bowl, use electric mixer on medium speed to beat butter and sugar until light and fluffy, about 2 min. Beat in eggs one at a time, incorporating each fully before adding next. Beat in vanilla. With mixer on low speed, alternately mix in the dry mixture in 3 parts with the buttermilk mixture in 2 parts, starting and ending with the dry mixture. Scrape the bowl as needed between additions.
Scrape batter into 2 greased and parchment-lined 9-in. (23-cm) round cake pans, smoothing the tops. Bake 30 to 35 min. until a tester comes out clean when inserted into centre of cake. Let stand 10 min. before running a sharp knife around edge and turning cake onto wire rack to cool completely.
Remove parchment paper.
Meanwhile, use electric mixer (clean beaters) beat the cream cheese until smooth then beat in the 1/2 cup (125 mL) butter until light and fluffy. Beat in icing sugar and vanilla just until smooth. Cut each cake horizontally into 2 layers. Place 1 layer on a serving platter; spread top with about 3/4 cup (175 mL) icing. Repeat process twice more. Top with last cake layer; spread remaining icing on top. Refrigerate at least 1 hr. to set icing before serving. Gather crumbs accumulated on platter to sprinkle on top to decorate cake. (Tip: Use a heart-shaped stencil for the crumb sprinkling when making cakes to celebrate loved ones.)
Using cold instead of room temperature cream cheese will keep frosting thick so it won’t need as much icing sugar to be easily spreadable; just make sure to beat the cheese until smooth before adding