01 - In a skillet over medium heat, melt the butter. Add pecan halves and brown sugar; cook, stirring constantly, until pecans are evenly coated and fragrant, about 3 minutes. Remove from heat and carefully incorporate the Southern Comfort bourbon liqueur. Allow mixture to cool completely.
02 - In a saucepan, whisk together the whole milk, granulated sugar, cornstarch, and salt. Cook over medium heat, stirring continuously, until the mixture thickens and starts to bubble. In a separate bowl, lightly beat the egg yolks. Gradually whisk in about 1 cup of the hot milk mixture to the yolks, then return this blend to the saucepan. Continue cooking and stirring for 2 to 3 minutes until fully thickened. Remove from heat, stir in vanilla extract, let cool to room temperature, and then refrigerate.
03 - In a chilled mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract with an electric mixer until soft peaks form. Refrigerate until ready for assembly.
04 - In a large glass trifle bowl, arrange one-third of the chocolate cake cubes in an even layer. Distribute one-third of the bourbon-soaked pecans over the cake, followed by one-third of the vanilla pudding and one-third of the whipped cream. Repeat this layering process two more times, finishing with the remaining whipped cream as the top layer.
05 - Adorn the final whipped cream layer with extra toasted pecans and generous chocolate shavings. Refrigerate the assembled trifle for a minimum of 2 hours prior to serving to allow flavors to develop.