For the crust:
Place the cookies in a food processor and pulse until cookies are a fine crumb (alternatively, place the cookies in a resealable bag and smash with a rolling pin). Transfer to a medium bowl and add a large pinch of salt followed by butter, mixing to combine.
Transfer to a 9” pie plate or tart pan. Place in refrigerator and chill while you prepare the filling.
For the filling:
Bring Irish Cream, ½ the can of sweetened condensed milk and 1 cup heavy cream to a simmer in a medium pot over medium heat.
Whisk egg yolks and cornstarch together until no lumps remain. Slowly whisk in cream mixture to the egg yolks until everything is incorporated.
Pour mixture back into the pot and cook, whisking constantly, until the mixture has started to bubble and thicken considerably, 4–6 minutes.
Place chocolate in a large bowl. Pour thickened pastry cream over chocolate and let it sit a minute or two to melt. Whisk until all the chocolate is dissolved, then add 1 cup sour cream and a generous pinch of salt and whisk to blend.
Pour chocolate mixture into the prepared crust, smoothing the top. Refrigerate until completely set, at least 2 hours.
When ready to serve, whisk the remaining cup of heavy cream in a medium bowl until you’ve got medium-stiff peaks (the cream should stand up at the tip of the whisk). Whisk in remaining cup of sour cream and the remaining sweetened condensed milk.
Dollop on top of chilled chocolate pie before serving.