Preheat oven to 350°F (175°C) and grease a 9×13 inch baking pan.
In a bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt. In another bowl, mix buttermilk, oil, eggs, and vanilla until smooth. Combine both mixtures gradually while mixing.
Add boiling water to create a thin batter and pour into the prepared pan. Bake for about 30-35 minutes. Cool, then crumble into pieces.
Mix cherry pie filling in a bowl until well combined.
In a chilled bowl, whip heavy cream with powdered sugar and vanilla until stiff peaks form.
Layer crumbled cake, cherry filling, and whipped cream in a trifle bowl or individual glasses. Repeat layers until ingredients are used up.
Garnish with chocolate shavings and refrigerate for at least two hours before serving.