Preheat your oven to 350°F (175°C). In a mixing bowl, combine chocolate graham cracker crumbs, melted butter, and granulated sugar. Stir until well blended, then press firmly into a tart pan. Bake for 10 minutes or until set, then allow to cool completely.

In a small bowl, sprinkle unflavored gelatin over two tablespoons of cold water and let sit for 5 minutes. Microwave for 10-15 seconds until liquid, stirring until fully dissolved. Set aside to cool slightly.

Using a heatproof bowl over simmering water, melt white chocolate chips until smooth. Remove heat and mix in milk. Fold in dissolved gelatin and peppermint oil, ensuring temperature is below 85°F. Set aside to cool.

In a mixing bowl, add heavy whipping cream and powdered sugar. Beat on medium-high speed until medium-stiff peaks form (3-5 minutes). Gently fold whipped cream into the cooled chocolate mixture, maintaining lightness.

Spoon the mousse into the cooled crust and smooth the top. Cover with plastic wrap and chill in the refrigerator for at least 4 hours or overnight.

In a small saucepan, heat cream until bubbling around edges. Stir in bittersweet chocolate until smooth. Add light corn syrup and very warm water, mixing until glossy.

Pour the warm chocolate glaze over the mousse filling, allowing it to flow over the edges. Let the tart set at room temperature for about 1 hour before slicing.