Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
Cream the butter and sugar together in a large bowl until light and fluffy.
Beat in the eggs one at a time, then mix in cinnamon, vanilla extract, and salt.
Add cocoa powder, red food coloring, and water to the batter, mixing until evenly combined.
Sift together the cake flour and baking powder.
Alternately add the sifted flour mixture and buttermilk to the batter, beginning and ending with the flour. Mix gently after each addition to combine.
In a small bowl, combine baking soda and vinegar, then fold this mixture into the batter.
Divide the batter evenly between the prepared cake pans and smooth the tops.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely before frosting or serving.