Preheat your oven to 350°F (175°C). In a mixing bowl, combine crushed chocolate graham crackers, melted butter, and sugar until well-blended. Press this mixture firmly into the bottom and up the sides of a tart pan. Bake for 10 minutes or until slightly set and fragrant. Remove from the oven and let the crust cool completely on a wire rack.

While the crust cools, bloom the unflavored gelatin in a small bowl with cold water for about 5 minutes. After blooming, gently heat in the microwave until fully dissolved. In a saucepan, melt the white chocolate chips over low heat and mix in the heated milk using a whisk. Once combined, fold in the dissolved gelatin and peppermint oil. Allow this mixture to cool to approximately 85°F (29°C).

In a separate mixing bowl, beat the heavy whipping cream and powdered sugar until medium-stiff peaks form. This should take about 3-5 minutes on high speed. Carefully fold one-third of the whipped cream into the cooled chocolate mixture to lighten it, then gently fold in the remaining whipped cream until fully combined.

Spoon the prepared peppermint mousse into the cooled chocolate graham cracker crust, spreading it evenly to the edges. Cover with plastic wrap and refrigerate overnight, allowing the mousse to set and flavors to meld beautifully.

On the day of serving, prepare the glaze by heating heavy cream in a saucepan until it reaches a boil. Remove from heat and stir in the bittersweet chocolate until melted and smooth. Then, mix in light corn syrup and warm water to achieve a glossy consistency. Pour the glaze over the chilled mousse, tilting the tart to cover the surface evenly.

Let the Dark Chocolate Peppermint Mousse Tart sit at room temperature for at least 1 hour after glazing to allow the glaze to set perfectly. Before serving, garnish with crushed candy canes for a festive touch. Slice and enjoy this indulgent, refreshing treat.