01 - Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - Combine chocolate cookie crumbs and melted butter in a medium bowl. Mix until well combined. Press the mixture firmly into the bottom of the prepared pan to form an even crust. Set aside.
03 - Melt the white chocolate chips in a heatproof bowl over a pan of simmering water (double boiler), stirring until smooth.
04 - Beat the cream cheese in a separate large bowl until smooth and creamy.
05 - Add the melted white chocolate, sweetened condensed milk, Irish cream liqueur, peppermint extract, and salt to the cream cheese. Beat until well mixed and silky. If desired, mix in a few drops of green food coloring until the color is evenly distributed.
06 - Pour the cheesecake fudge mixture over the prepared crust. Smooth the top with a spatula. Refrigerate for at least 3 hours, or until set and firm.
07 - Once set, drizzle with melted dark chocolate and sprinkle with green decorations, if using. Lift fudge out of the pan using parchment overhang. Cut into 16 squares with a sharp knife, wiping the blade clean between cuts.