Preheat oven to 350°F (175°C). Grease a 9-inch springform pan or deep pie dish generously with butter or nonstick spray, then line the bottom with parchment paper.

Prepare the streusel topping. In a medium bowl, combine chopped pecans, brown sugar, granulated sugar, flour, cinnamon, and nutmeg. Pour in melted butter and stir until the mixture is crumbly and evenly coated. Add crystallized ginger if using. Spread this mixture evenly over the bottom of the prepared pan.

Make the pumpkin layer. In another bowl, whisk together pumpkin puree, brown sugar, eggs, vanilla extract, cinnamon, ginger, nutmeg, cloves, and salt. Slowly whisk in evaporated milk and heavy cream until the filling is smooth and blended. Set aside.

Prepare the spice cake batter. In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, ginger, and cloves. In a large mixing bowl, beat softened butter and brown sugar until light and fluffy, about 2 minutes. Add eggs one at a time, mixing well after each. Stir in vanilla extract and sour cream until combined. Gradually add the dry ingredients, mixing until the batter is smooth and thick.

Assemble the layers. Gently spread the spice cake batter over the streusel layer in the pan. Carefully pour the pumpkin filling over the cake batter, spreading evenly. The pumpkin mixture may sink slightly, which is normal.

Bake for 55–65 minutes, or until the center is mostly set and a toothpick inserted into the cake portion comes out clean. The top should look firm and slightly golden around the edges.

Cool in the pan for 15 minutes. Run a thin knife around the edges to loosen the sides. Place a large serving plate on top of the pan and carefully invert. Lift off the pan and peel away the parchment paper if needed. The pecan streusel will now be on top.

Let the dessert cool completely before slicing. Serve slightly warm or chilled with whipped cream or vanilla ice cream.

Store leftovers covered in the refrigerator for up to 4 days.