1 pound (450g) mascarpone, softened
3/4 cup granulated sugar
3/4 cup heavy whipping cream
1/2 cup plus 2 tablespoons plus 1/2 cup Irish Cream such as Bailey's or Carolan's, divided
8 ounces Guinness
36 savoiardi (Italian ladyfingers)
Small bar good-quality chocolate, for shaving
Combine the mascarpone and sugar in a medium bowl, stir vigorously to dissolve sugar. Place whipping cream and 2 tablespoons Irish Cream in a stand mixer fitted with a whisk attachment. Whip on high until stiff peaks form, 2-3 minutes. Gently fold whipped cream into mascarpone.
Pour Guinness into a shallow bowl. One at a time, dip ladyfingers into Guinness on each side. Don't soak them: counting to one on each side will provide all the stout flavor and moisture you'll need. Place in a tight single layer in dish, breaking them into pieces as necessary. Drizzle 1/4 cup Irish Cream over entire layer. Pour about 1-2 cups of the mascarpone mixture over ladyfingers until covered, spreading smooth with a spatula. Grate a layer of chocolate shavings over the top with a microplane or a vegetable peeler.
Repeat process with another layer. Refrigerate for at least 12 hours or overnight before serving.