Preheat oven to 350F, Line a large baking sheet with parchment paper, spray with pan spray. Set aside.
In a large bowl, combine the flour, cocoa, baking powder, baking soda, and salt. Set aside.
In a separate bowl, whisk together sugar, eggs, buttermilk, and vanilla until well combined and smooth. Add a little red food colouring, mix well to combine, then pour into the bowl with the dry mixture, stir to combine.
If you want more red food colouring, add it now and stir gently to combine.
Divide dough in half, form into 2 long, wide loaves on the prepared pan.
Bake for 20-25 minutes, until golden brown on the outside. Remove from oven, turn heat down to 250F.
Allow loaves to cool for 5 minutes.
Cutting on a slight diagonal, slice each loaf into ½" slices.
Arrange slices on the pans. Bake for 15 minutes, flip each piece over and bake for another 15 minutes, or until desired texture.
Remove from oven, allow to fully cool.