Preheat oven to 350F. Unroll pie crust and place it into pie plate. Chill until ready to fill.
Whisk butter and cocoa. Whisk in eggs. Add sugar, salt, vanilla, and flour and whisk until smooth. Gently whisk in milk. Stir in peppermint crunch baking pieces.
Pour batter into prepared pie shell. Bake for 40-45 minutes until it’s just slightly jiggly in the center and no longer dull on top. Cool completely before topping.
Serve with whipped cream or Cool Whip and more peppermint crunch pieces and/or crushed candy canes.
I find the Andes Peppermint Crunch baking pieces at Super Walmart. They also sell the Peppermint Crunch patties (like regular Andes mints) at the grocery store in the holiday section. If you cannot find them you can use regular Andes mints, or any peppermint bark candy (like Ghiradelli, Nestle, or any brand you find).