With the rack in the middle position, preheat the oven to 350°F (180°C). Butter and flour two 8-inch (20 cm) springform pans. Line the bottoms with parchment paper.
In a bowl, whisk together the flour, baking powder, baking soda and salt. Set aside.
In another bowl, combine the cocoa powder, vinegar, vanilla and food colouring.
In a large bowl, cream the butter, sugar and red cocoa mixture with an electric mixer. Beat in the eggs, one at a time, until smooth. With the mixer at low speed, stir in the dry ingredients alternately with the buttermilk. Divide the batter equally between the prepared pans.
Bake for 35 minutes or until a toothpick inserted into the centre of the cakes comes out clean. Let cool completely on
a wire rack. Unmould.
Cut off the rounded tops of each cake and finely crumble onto a parchment-lined baking sheet. Spread the crumbs evenly. Bake for 15 minutes. Let cool completely.
In a food processor, pulse the crumbs to the size of bread crumbs. Press through a sieve to obtain even finer crumbs. Set aside. Discard any larger crumbs that remain in the sieve.
In a small saucepan over medium heat, melt 2 tbsp of the butter. Add the flour and cook for 1 minute, whisking constantly. Add the milk and vanilla and bring to a boil, then simmer for 1 minute, still whisking constantly.
Pour the mixture into a bowl and cover with plastic wrap directly on the surface. Let cool completely.
Add the sugar, cream cheese and the remaining butter to the cooled mixture. Whip using an electric mixer until creamy and smooth, about 5 minutes.
Halve each cake horizontally to obtain 4 layers.
Spread 1/2 cup (125 ml) of the frosting onto each cake layer. On a parchment-lined baking sheet, stack the layers, then frost the whole cake.
Sprinkle the reserved cake crumbs over the entire cake, then lightly press them into the frosting. Use your hand to gently smooth the crumbs, giving the cake a velvety effect.
Using a large offset spatula, transfer the cake to a serving platter.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.