Begin by preparing the topping. In a medium saucepan, cook the brown sugar, butter, vanilla, and salt over medium heat, stirring constantly. Stir until smooth. Remove from the heat and then whisk in the flour until smooth. Transfer to a sheet of wax (or parchmenpaper. Cool completely.
Next, preheat your oven to 350 degrees Spray an 8-inch square baking pan (or 8x10-inch rectangular baking pawith cooking spray.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, cloves, and salt.
In a large bowl, whisk together the pumpkin, brown sugar, oil, eggs, sour cream, and vanilla. Add the flour mixture to the pumpkin mixture, whisking until just combined.
Pour the batter into the prepared pan. Then break the cooled topping into chunks/crumbs and sprinkle on top of the batter.
Bake for 40-45 minutes or until a toothpick inserted near the center comes out clean.