Cut or break the chocolate cake into 1-inch cubes. Place half the cake pieces into the bottom of a clear trifle dish or large bowl. Drizzle with 1½ tablespoons of Baileys Irish Cream, allowing the liqueur to soak into the cake.
In a large bowl, beat the cream cheese until smooth and creamy (approximately 2 minutes). Add sugar gradually while continuing to beat, then incorporate the Baileys and vanilla extract.
Gently fold in the whipped heavy cream using a spatial with a down-and-over motion rather than stirring, which preserves the airy texture.
Place 1 cup of the heavy cream in a microwave-safe bowl and heat until just simmering (about 90 seconds). Pour over chocolate chips and let stand for 2 minutes before whisking until completely smooth.
Allow the chocolate mixture to cool to room temperature (approximately 15 minutes), then stir in the Baileys Irish Cream.
In a separate bowl, whip the remaining heavy cream with powdered sugar until stiff peaks form, then gently fold into the cooled chocolate mixture.
Spread half of the cheesecake mixture over the soaked cake layer, ensuring even coverage. Follow with half of the chocolate mousse layer.
Repeat the process with remaining cake (drizzled with remaining Baileys), cheesecake mixture, and chocolate mousse.
Top the trifle with whipped cream (1 cup heavy cream whipped with 2 tablespoons powdered sugar), creating decorative peaks if desired.
Sprinkle generously with chocolate shavings, dust lightly with cocoa powder, and add fresh berries around the edge if desired.
Refrigerate for at least 4 hours, preferably overnight, before serving.