Preheat oven to 350°F (175°C). Grease a 9-inch springform pan and line the bottom with parchment paper.
In a bowl, combine graham cracker crumbs, melted butter, and sugar. Press the mixture into the bottom of the pan.
Bake crust for 8 minutes, then let cool slightly.
In a saucepan over low heat, stir together sweetened condensed milk and cocoa powder until smooth. Pour over the crust and spread evenly.
Sprinkle chocolate chips and toffee bits over the top.
Bake for 20–25 minutes, then let cool completely.
Whip heavy cream with powdered sugar and vanilla until stiff peaks form. Spread whipped cream over cooled cake.
Decorate with holiday candies or sprinkles if desired. Chill before serving.