To make cake, preheat oven to 350 degrees and spray 2 9-inch cake pans with baking spray with flour. (Or butter pans and then lightly coat with flour.)
In a large mixing bowl (one that fits an electric mixer) combine flour, sugar, cocoa powder, baking soda, and salt.
In a medium bowl, whisk together buttermilk, vegetable oil, eggs, and vinegar.
With the mixer on low, add the buttermilk mixture to the flour mixture. Once all buttermilk mixture has been added, turn to medium speed and beat until smooth.
Add food coloring and beat until mixed evenly.
Divide batter evenly between the two prepared pans and bake 18 to 22 minutes. Let cool in pans for 10 minutes and then remove to wire rack to cool completely.
To make cream, in a medium bowl whisk together pudding mix and milk. Refrigerate for 5 minutes. Fold in whipped topping until evenly combined.
To assemble trifles, either use 10 individual bowls or one big bowl. Alternate layering crumbled cake (I use my hands to crumble it or you can cut it into chunks with a knife) with the cream filling, finishing with filling. Store in refrigerator. Will keep for 2-3 days.