Pastry: In bowl, whisk together flour, cocoa powder, cinnamon, ginger, salt, nutmeg and cloves. Using pastry blender or 2 knives, cut in butter and lard until mixture resembles coarse crumbs with a few larger pieces.
Whisk together ice water, sour cream and egg; drizzle over flour mixture, tossing with fork and adding up to 1 tsp more ice water if necessary to form ragged dough. Divide dough in half; shape into discs. Wrap each in plastic wrap; refrigerate until chilled, about 1 hour. (Make-ahead: Refrigerate for up to 3 days or freeze for up to 1 month.)
On lightly floured work surface, roll out 1 of the pastry discs to generous 1/4-inch thickness; fit into 9-inch pie plate. Trim to fit, leaving 1-inch overhang; fold overhang under. Prick bottom and side of crust all over with fork.
Roll out remaining pastry disc to 1/4-inch thickness. Using 1 1/2-inch gingerbread man cookie cutter, cut out enough shapes to cover rim of crust, rerolling scraps as necessary. Reserve remaining dough for another use.
Whisk egg yolk with 2 tsp water; brush over rim of pastry. Arrange shapes around rim to cover, gently pressing to adhere. Refrigerate until firm, about 30 minutes.
Line crust with foil and fill with pie weights or dried beans. Bake on bottom rack of 400°F oven for 20 minutes. Remove pie weights and foil; bake until no longer shiny, about 10 minutes. Let cool completely.
Custard: While crust is chilling, in heatproof bowl, whisk together egg yolks, 1/2 cup of the milk, the sugar, cornstarch, molasses, cinnamon, ginger, nutmeg and cloves.
In heavy-bottomed saucepan, heat remaining milk over medium heat just until bubbles form around edge; gradually whisk into egg yolk mixture. Return to saucepan; cook over medium heat, whisking constantly, until thick enough to mound on spoon, 3 to 4 minutes. Strain through fine-mesh sieve into bowl; stir in vanilla. Place plastic wrap directly on surface. Refrigerate until chilled, about 1 hour. (Make-ahead: Refrigerate for up to 24 hours.)
Beat cream until stiff peaks form; fold into custard. Spoon into crust, smoothing top; cover loosely with plastic wrap. Refrigerate for 4 hours. (Make-ahead: Refrigerate for up to 12 hours.)
Topping: In bowl, beat cream until soft peaks form; beat in sugar and vanilla. Spoon over custard, leaving 2-inch border uncovered. Dust with cinnamon.
Tip from The Test Kitchen: Roll out reserved dough to 1/4-inch thickness. Using 1 1/2-inch gingerbread man cookie cutter, cut out shapes, rerolling scraps as necessary. Arrange, 1 inch apart, on parchment paper–lined rimless baking sheet; sprinkle with 1 tbsp granulated sugar. Refrigerate until firm, about 15 minutes. Bake in 400°F oven until no longer shiny, about 8 minutes. Let cool on pan for 2 minutes; transfer directly to rack to cool completely.