Crust

1. Preheat oven to 350F/180C and grease a 9-inch tart pan with a removable bottom.
2. Combine crushed Oreos and melted butter. Press into the tart pan and bake for 8 minutes. Remove and let cool on a wire rack as preparing the filling.

Filling

1. In a medium saucepan whisk together the reduced Guinness, milk, cream, Dorda Liqueur, brown sugar, cocoa powder, and cornstarch. Whisk until full combined then place over medium-low heat. Bring to a boil then let simmer whisking constantly for 2-3 minutes.
2. Remove saucepan from heat and whisk in the chopped chocolate and vanilla. Whisk until smooth. Pour on top of Oreo crust. Place a piece of plastic wrap directly on top of the filling to prevent a skin from forming. Chill for 3 hours to set the chocolate filling.

Boozy Whipped Cream

1. In the bowl of an electric mixer fitted with a whisk attachment or large bowl with a handheld whisk combine heavy whipping cream, Dorda Liqueur, and powdered sugar until stiff peaks form. Spread on top of the chilled tart and use a Microplane zester to grate chocolate on top or drizzle with salted caramel sauce. Store in the fridge for up to three days.