Preheat your oven to 350°F (175°C). In a mixing bowl, combine crushed chocolate graham crackers, melted unsalted butter, and sugar until the mixture resembles wet sand. Press the mixture firmly into the bottom and up the sides of a tart pan. Bake for 10 minutes, and then let it cool completely before filling.

In a small bowl, bloom the unflavored gelatin in cold water for about 5 minutes. Once bloomed, microwave it for 10–15 seconds until fully dissolved. Meanwhile, melt the white chocolate chips with the milk in a heatproof bowl over simmering water, stirring until smooth. Mix in the cooled gelatin and peppermint oil until well combined.

In a separate large mixing bowl, beat the heavy cream and powdered sugar using an electric mixer until medium-stiff peaks form, about 3-5 minutes. Gently fold the whipped cream into the chocolate mixture using a spatula. Be careful not to deflate the whipped cream.

Pour the mousse into the cooled chocolate graham cracker crust, smoothing the top with a spatula. Cover the tart and refrigerate for at least 4 hours, or overnight for best results.

Heat the heavy cream in a saucepan over medium heat until it starts to boil. Remove from heat and add the chopped bittersweet chocolate, stirring until completely melted and smooth. Stir in light corn syrup and warm water.

Once the mousse has set, carefully pour the warm chocolate glaze over the tart, using an offset spatula to spread it evenly. Allow the tart to sit at room temperature for about 1 hour before slicing and serving.