Step 1

For custard: Adjust oven rack to middle position and preheat oven to 425°F. In a medium bowl, whisk together sugar, cinnamon, nutmeg, ginger, cloves, allspice, salt, and citrus zest. Set aside.

Step 2

In a large bowl, whisk together pumpkin and eggs. Whisk in spice mixture. Whisk in evaporated milk. Pour pumpkin mixture into baking dish and bake for 15 minutes. Reduce heat to 350°F and bake until mixture is just set (it will be slightly jiggly in the center but will firm as it cools), about 45 minutes. Let cool completely. Do not turn off the oven.

Step 3

For cookie crumble: While custard is cooling, mix together cookie crumbs, dark brown sugar, salt, and flour. Add melted butter and mix until well coated. Press into bottom of pie dish and bake until cookies are toasted and fragrant and mixture holds together, 10-15 minutes. Let cool completely.

Step 4

To serve: Break up cookie crumble into large shards. Top each serving of custard with crumble and whipped cream, if desired. Store leftover custard in the refrigerator. Keep crumble separately at room temperature in an airtight container.