Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
In another bowl, beat together sugar, oil, eggs, and vanilla extract until smooth. Gradually add dry ingredients, alternating with buttermilk, until well combined.
Divide batter evenly between prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
For the filling and topping, beat heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
Place one cake layer on a serving plate. Spread with half of the whipped cream and top with cherry pie filling. Place the second cake layer on top and spread remaining whipped cream over the top and sides of the cake. Garnish with chocolate shavings.