Preheat your oven to 350°F (175°C). In a mixing bowl, combine crushed chocolate graham crackers, melted butter, and sugar until moistened. Press evenly into a tart pan. Bake for 10 minutes, then cool for at least 15 minutes.

In a small bowl, bloom unflavored gelatin in cold water for 5 minutes. Gently heat until fully dissolved. Melt white chocolate chips in the microwave, stir in warm milk, then mix in dissolved gelatin and peppermint oil. Cool to about 85°F.

Beat heavy whipping cream and powdered sugar until medium-stiff peaks form (about 3-4 minutes). Fold whipped cream into the chocolate-peppermint mixture in three stages.

Spoon the mousse into the cooled crust, smooth the top, cover with plastic wrap, and refrigerate for several hours or overnight.

In a saucepan, heat heavy whipping cream until boiling, remove, and stir in chocolate until smooth. Mix in corn syrup and warm water until pourable.

Pour the glaze over the tart when set, let sit at room temperature for about an hour to set before serving.