Preheat oven to 350 degrees and grease 2 9-inch cake pans with Crisco. (Or use baking spray.)
Combine brown sugar, butter, and 3 tablespoons heavy cream in a medium saucepan. Heat over medium heat, stirring frequently until butter is melted and sugar has dissolved.
Divide mixture evenly between the 2 cake pans. Sprinkle 1/2 cup pecans into each pan. Let cool while you make cake batter.
In a large bowl, use an electric mixer to beat eggs, sugar, and oil.
Mix in vanilla extract and pumpkin.
In a medium bowl, whisk together flour, baking powder, baking soda, cinnamon, ginger, nutmeg, allspice and salt.
Gradually add flour mixture to pumpkin mixture until just blended.
Use a spoon and drop batter by spoonfuls over the brown sugar mixture, dividing the batter evenly between the pans.
Bake for 30 to 35 minutes. Set a baking sheet beneath the pans because a little batter may overflow.
Let cakes cool in pans for 5 minutes and then invert onto cooling racks to cool completely. If you let them cool too long in the pans, they will start to stick.
Make Whipped Cream. Beat heavy cream until it begins to thicken. Add powdered sugar and vanilla and beat until stiff peaks form.
Place 1 cake layer on a cake stand, pecan side up. Spread 3/4 of whipped cream on top. Top with the second layer.
Place remaining whipped cream in the middle of the top layer. Sprinkle with pecans. Store in refrigerator.