Line a 9x13 inch pan with parchment paper (bottom and two sides only, it will be easier to unmold), and spray or butter the unlined sides.
In a large bowl, beat 1 cup butter adding 2 cups light brown sugar gradually until very creamy, 2 to 3 minutes.
Add 2 eggs, one at a time, and beat well. Add 1 teaspoon vanilla extract and mix well.
Sift 2 cups all-purpose flour with 2 teaspoons baking powder, 1 teaspoon ground cinnamon, ½ teaspoon ground ginger, ½ teaspoon ground allspice and ½ teaspoon salt and add it in 2 parts to the butter mixture. Mix only until starting to blend.
Add 1 ½ cups pumpkin puree and mix well. Pour into the prepared pan, spreading evenly.
In a small bowl mix ½ cup sour cream (or cream cheese) with ¼ cup white sugar and 1 tablespoon heavy cream.
Drizzle on top of the pumpkin batter. Sprinkle 1 cup pecans on top and bake for about 30-40 minutes, until a tester comes out clean.
Let cool on wire rack. Remove carefully from the pan. Serve at room temperature.
It keeps at room temperature for 2 days and a week in the fridge covered in plastic wrap.
Notes
Pumpkin: as I mentioned above, I use homemade pumpkin puree but use the canned variety, unsweetened. So much easier!Spice mix: I make my pumpkin spice mix but you can use one you like already. If you have never used them together, take this recipe as a guide and adjust individual spices to your liking.Nuts: pecans are the traditional pair with pumpkin, but walnuts work very well too. Use hazelnuts if you want to innovate. Another option is to omit the nuts.Cheese: cream cheese makes a thicker swirl, and sour cream makes it slightly more fluid.Storing: the cake keeps at room temperature for a couple of days. You can freeze it for a few weeks, well wrapped. Defrost at room temperature.