Preheat the oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving some overhang for easy removal later.

In a mixing bowl, combine the chocolate cookie crumbs, melted butter, sugar, and a pinch of salt. Mix until well combined. Press this mixture firmly into the bottom of the prepared pan. Bake for 12-15 minutes until set, and let it cool completely.

In a medium saucepan, whisk together the sugar, cornstarch, and cocoa powder. Gradually whisk in the milk and heavy cream until smooth. Add in the egg yolks and place the saucepan over medium heat, stirring continuously until the mixture thickens (about 5-7 minutes). Remove from heat, then stir in the chopped dark chocolate, vanilla, and butter until melted and smooth. Spread this chocolate mixture evenly over the cooled crust, then cover and refrigerate until set (about 2 hours).

In a mixing bowl, beat the softened cream cheese until smooth. Gradually add in the powdered sugar and vanilla extract, mixing until creamy. In another bowl, whip the chilled heavy whipping cream to stiff peaks, then gently fold it into the cream cheese mixture until fully combined. Spread this vanilla cream layer over the chocolate, smoothing it out gently. Chill for at least 1 hour.

In a small saucepan, heat the heavy cream until it just begins to steam. Pour it over the chopped semi-sweet chocolate, letting it sit for about 3-5 minutes to allow the chocolate to melt. Stir until smooth and pour over the vanilla layer. Refrigerate until the ganache is set (approximately 30 minutes).

Once fully set, lift the bars from the pan using the parchment paper. Cut them into squares and garnish with chocolate curls, a dusting of cocoa powder, or whipped cream if desired.