In a mixing bowl, whisk together the brown sugar, salt, cinnamon, and flour. Add the butter, and with your hands, combine everything until it is well incorporated. You want it to have a shaggy look. Set aside. This can be made ahead of time and can be stored in an air tight container for up 5 days.
For the pumpkin cake
Preheat your oven to 325 degrees. Spray a 9×13 metal pan on the bottom, line with parchment paper, and spray again. If you need to use metal binder clips to hold down the sides, remember to use metal, not plastic. Set aside.
In a medium sized bowl, combined the flour, baking powder, cardamon, ground cinnamon, ginger, nutmeg, and salt. Set aside.
In a stand sized mixer fitted with the paddle attachment, cream the sugar and eggs on medium speed until they are light and fluffy, about 4 minutes.
Add the oil and vanilla and beat on medium until fully incorporated, about 30 seconds. Add the pumpkin puree and mix until combined, about 30 seconds.
With the mixer on the lowest speed, gradually add the dry ingredients to the pumpkin/egg mixture.
Evenly distribute the pumpkin batter to the prepped cake pan. With the back of a spoon, even out the batter to ensure it’s smooth for baking.
Evenly sprinkle the cinnamon topping on top of the pumpkin cake batter.
Bake for 35-38 minutes. Check the cake by inserting a toothpick. It’s done when it comes out with just a few moist crumbs on it.
Let it completely cool in the cake pan. While the cake cools, make the brown sugar glaze
For the glaze
In a small saucepan combine butter, brown sugar and milk on medium heat. Bring the mixture to a simmer, whisking frequently and cook until the sugar is dissolved, a minute or two. Remove from the heat and cool for 5 minutes.
Add vanilla, whisking to combine. Add all of the powdered sugar whisking vigorously, until you reach your desired consistency. The glaze will start to firm up quickly so have the cake ready. Immediately drizzle the glaze over the cake. It will start to set on the cake. If the glaze is starting to set faster, you can always heat it up in the microwave.