01 - Line an 8x8-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal of the finished squares.
02 - Combine chocolate cookie crumbs and melted butter in a medium bowl. Mix until evenly moistened and press firmly into the bottom of the prepared pan to create an even crust layer.
03 - Set up a double boiler by placing a heatproof bowl over a pan of simmering water. Add white chocolate chips and stir continuously until completely melted and smooth.
04 - In a large mixing bowl, beat the softened cream cheese with an electric mixer until completely smooth and creamy, about 2 minutes.
05 - Pour the melted white chocolate, sweetened condensed milk, Irish cream liqueur, peppermint extract, and salt into the cream cheese. Beat on medium speed until fully incorporated and silky. Add green food coloring drop by drop if desired and mix until uniform color is achieved.
06 - Pour the cheesecake fudge mixture over the prepared crust. Use a spatula to spread evenly and smooth the top surface.
07 - Refrigerate for at least 3 hours or overnight until completely firm and set throughout.
08 - Once fully set, drizzle melted dark chocolate over the surface and immediately sprinkle with green decorations if using.
09 - Lift the squares from the pan using the parchment overhang. Use a sharp knife to cut into 16 equal squares, wiping the blade clean between cuts for neat edges.