Whip: In a large mixing bowl, add the cold heavy cream, sugar, Irish cream, vanilla extract, and vanilla instant pudding, and whip with an electric hand mixer until soft peaks form.
Add the Mascarpone: Add the room temperature mascarpone and mix just until smooth and creamy. Don't overmix, or it may curdle.
Assemble the tiramisu
Dip: Mix the espresso and Irish cream in a shallow bowl. Dip each ladyfinger for 1 to 2 seconds and lay them in an even layer in a 9x13-inch dish.
First Layer: Spread half of the mascarpone cream over the ladyfingers.
Second Layer: Add another layer of dipped ladyfingers and spread a thin layer of cream on top.
Pipe: Pipe the remaining cream in dollops all over the top with a round tip.
Chill and Dust: Cover and chill for at least 4 hours. Dust generously with cocoa powder just before serving.
Notes
Cold Cream: Use very cold heavy cream so it whips into stable peaks.
Room Temperature Mascarpone: Blends smoothly without lumps.
Don't Overmix: Stop once the mascarpone is combined so the cream doesn't curdle.
Cooled Espresso: Warm coffee makes the ladyfingers mushy.
Quick Dip: 1 to 2 seconds per ladyfinger is enough.
Powdered Sugar: Can replace the granulated sugar by weight (150 g).
Non-Alcoholic: Use Irish cream coffee creamer instead of the liqueur.
Smaller Pan: Make half the recipe for an 8 or 9-inch square dish.
Make Ahead: Assemble up to 2 days ahead and dust with cocoa before serving.
Storage: Keep covered in the fridge for up to 4 days, or freeze for up to 1 month.