4 cups mini pretzels, for crust
4 tablespoons granulated sugar, for crust
8 tablespoons unsalted butter, melted, for crust
1 large egg yolk, for filling
1 1/2 cups whole milk, for filling
1 cup heavy cream, for filling
1/4 cup sugar, for filling
6 ounces quality milk chocolate, chopped (such as Lindt), for filling
2 tablespoons Dutch-process cocoa powder, for filling
1 teaspoon vanilla extract, for filling
2 tablespoons cornstarch, for filling
Crushed pretzels, for filling
Pinch salt, for filling
To make the crust: Heat oven to 350 degrees.
Grind pretzels in food processor until fine crumbs with a few larger bits remain. Combine pretzels with sugar (3 tablespoons); stir in melted butter.
Press crumb mixture into a 9-inch pie plate. Bake until edges are golden and crust looks dry, 17 to 20 minutes. Cool on rack to room temperature.
To make the filling: Sift sugar, cocoa, cornstarch, and salt into a medium saucepan.
Slowly whisk in about ½ cup milk, whisking constantly until dry ingredients are fully incorporated and mixture is completely smooth; whisk in egg yolk.
Whisk in remaining milk and ¼ cup heavy cream.
Place saucepan over medium heat and cook, whisking constantly, until milk mixture come to a gentle boil.
Boil 1 minute, whisking constantly, then remove from heat and add chopped chocolate to pan, stirring until it is completely melted and smooth; stir in vanilla.
Pour chocolate mixture into pie shell. Place in refrigerator, uncovered, until completely cool. Cover with plastic wrap and chill at least 8 hours or overnight.
To make the garnish: Whip ¾ cup heavy cream and 1 teaspoon sugar to soft peaks. Spread over chilled pie and sprinkle with a few crushed pretzels. Serve immediately.