Melt the chocolate in a double boiler or microwave, stirring frequently until smooth.
In a separate bowl, whip the heavy cream with the sugar and vanilla until stiff peaks form.
Fold the whipped cream into the melted chocolate until well combined.
Line a springform pan with graham cracker crumbs and press into the bottom and up the sides.
Pour the chocolate mousse into the prepared pan and smooth the top.
Refrigerate for at least 4 hours or until set.
Serve chilled.
