Make the crust: preheat oven to 350°F. Cream butter and sugar together. Mix in salt and espresso powder. Melt chocolate and cool to room temperature; blend into butter. Fold in flour until crumbly.
Spread crumbs on a sheet pan and bake 15 minutes. Cool completely, then pulse in a food processor. Transfer to a bowl, blend in melted butter, and press evenly into a pie tin. Bake 5 minutes to set. Cool.
Make the custard: combine milk and sugar in a saucepan and bring to a simmer. Whisk together egg yolks and cornstarch. Gradually blend in the hot milk, return to the pot, and bring to a simmer whisking constantly.
Simmer 1 minute, remove from heat, and beat in chocolate chips, butter, and vanilla. Pour hot custard into crust. Press plastic film onto the surface and refrigerate about 2 hours.
Whip cream with sugar to firm peaks. Pipe or spread over the chilled pie to cover completely. Serve cold.
