- To make the crust: Pulse the cookies in a food processor until finely chopped. Add the butter and mix until the cookie crumbs are evenly moistened. Press the mixture across the bottom and 1" up the sides of a lightly greased 9" or 10" springform pan. Refrigerate to set the crust.
- To make the filling: Whisk the egg yolks with 1/4 cup of the sugar in a medium mixing bowl over 1" of simmering water, until the mixture is light-colored and thick, able to hold a ribbon as it drops off the whisk back into the bowl. This will take 3 to 4 minutes; be sure to whisk continuously. Remove from the heat.
- In a separate bowl, beat the cream cheese with the remaining 1/4 cup sugar until fluffy and completely smooth. Whisk into the warm egg mixture; then add the Irish whiskey cream liqueur and mix until evenly combined.
- In a small heatproof dish, combine the gelatin and water; let sit for 3 minutes. Heat gently over hot water or at low power in the microwave in 10-second bursts, swirling until dissolved. Whisk the dissolved gelatin into the cream cheese mixture.
- Whip the heavy cream to soft peaks and fold it in. Pour the filling mixture on top of the crust in the pan and use a small offset spatula to smooth the top. Chill, uncovered, for at least 1 1/2 hours, until set.
- To unmold the cake: Run a thin spatula around the edge of the pan to free the cake before unclipping the pan and removing the side. Cool the cake completely.
- To make the topping: Heat the cream and chocolate together over low heat, stirring until the mixture is smooth. Pour into a pool in the center of the cake, as shown; or drizzle over the top and down the sides.
- Store any leftovers, well wrapped, in the refrigerator for several days.