Step 1

Make the crust: Preheat oven to 350 degrees. Combine graham cracker crumbs, butter, sugars, salt, and cinnamon in bowl. Firmly press mixture into bottom and up sides of a deep, 9 1/2-inch pie dish. Bake until firm, 8 to 10 minutes.

Step 2

Remove from oven, and sprinkle bittersweet chocolate over bottom of crust. Return to oven to melt chocolate, about 1 minute. Spread chocolate in a thin layer on bottom and up sides. Let cool on a wire rack. Reduce oven temperature to 325 degrees.

Step 3

Make the filling: In a large heatproof bowl set over a pot of simmering water, melt semisweet chocolate and butter, stirring until smooth. Remove from heat.

Step 4

Mix pumpkin, milk, brown sugar, eggs, cornstarch, vanilla, salt, cinnamon, ginger, nutmeg, and a pinch of cloves in a medium bowl. Whisk 1/3 pumpkin mixture into chocolate mixture. Whisk in remaining pumpkin mixture until completely incorporated.

Step 5

Transfer pie dish to a rimmed baking sheet, and pour pumpkin mixture into crust. Bake until center is set but still a bit wobbly, 55 to 60 minutes. Let cool in pie dish on a wire rack. Refrigerate until well chilled, at least 8 hours (preferably overnight). Before serving, drizzle melted milk chocolate on top. Serve immediately.