Preheat the oven to 350°F.

In the bowl of a food processor, pulse graham crackers to a very fine crumb. Add to a medium bowl along with ⅓ cup sugar and melted butter; stir with a spatula until combined. Using the bottom and sides of a measuring cup or with your fingers, press the graham cracker mixture firmly and evenly into the bottom and sides of a 9-inch pie pan.

Bake for 8 to 10 minutes or until crust is lightly golden and just set; set aside to cool for 10 minutes. Increase oven temperature to 425°F.

While the crust bakes, prepare filling. In a large bowl, whisk together pumpkin puree, eggs and ¾ cup sugar until combined. Add cinnamon, ginger, nutmeg and salt; whisk to combine. Whisk in evaporated milk until incorporated.

Pour filling into slightly cooled crust. Bake pie at 425°F for 15 minutes; reduce oven temperature to 350°F, and bake for an additional 35 to 45 minutes more or until the filling is set along the edges and only slightly jiggly in the center. Cover the crust during baking if it's getting too brown.

Transfer baked pie to a cooling rack to cool completely, about 2 hours.

Add semisweet chocolate to a medium bowl. Pour heavy cream into a microwave-safe measuring cup; microwave on High 30 seconds or until very hot but not yet boiling. Pour hot cream over chocolate in bowl; stir with a spatula until the mixture is smooth. Set aside for 10 minutes to cool and thicken.

Pour and spread cooled ganache topping over top of cooled pie to within ½-inch of the edges. Refrigerate 30 minutes, uncovered, or until ganache is set.

Add milk chocolate chips to a small, microwave-safe bowl. Microwave on High 30 seconds; stir, then continue to heat on High in 10-second intervals, stirring after each, until chocolate is melted and smooth. Use a spoon or piping bag to drizzle chocolate over pie.

Serve immediately, or allow chocolate to set before serving.