Preheat your 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. Combine wet ingredients in another bowl; mix until smooth. Gradually combine both mixtures and add boiling water last.
Pour batter into the prepared pan and bake until done (about 30 minutes). Cool before crumbling into pieces.
Mix cherry pie filling in a medium bowl.
Whip chilled cream until soft peaks form; gradually add powdered sugar and vanilla until stiff peaks develop.
In a trifle bowl or individual serving glasses, layer crumbled cake, cherry filling, and whipped cream three times.
Garnish with chocolate shavings and maraschino cherries. Chill for at least two hours before serving.