1. Preheat the oven to 350 degrees F. Spray a rimmed half-sheet pan (18X13) with nonstick cooking spray. 
2. In a bowl, whisk together the flour, baking soda, cinnamon, and salt. Set aside.
3. In a large bowl, with a handheld or stand mixer beat the butter, cane sugar, and brown sugar on high speed until combined and large crumbs form, scraping down the sides with a rubber spatula.
4. Add pumpkin puree, sour cream, eggs, and vanilla. Beat on medium-high speed until combined, scraping down the sides as needed.
5. With the mixer on low speed, add the dry ingredients to the wet, mixing until combined.
6. Pour the batter into the greased sheet pan, spreading out the batter evenly with a spatula. Bake for 25-27 minutes or until toothpick inserted in the center of the cake comes out clean. Remove the cake from the oven and set it on a wire rack. Allow to cool completely in the pan.

Brown Butter Cream  Cheese Frosting

1. In a light-colored pan, melt butter over medium heat, stirring occasionally. Once butter is melted it will begin to foam. After about 5 minutes the butter will begin to brown. There should be lightly brown specks on the bottom of the pan and it will have an intense nutty smell. Immediately remove the pan from the heat and transfer the brown butter into a bowl. Set aside to cool slightly.
2. In the meantime, beat the cream cheese with a handheld or stand mixer until smooth and creamy.
3. Add half of the confectioners’ sugar and beat on low speed until creamy, scraping down the sides as needed. Then add the remaining confectioners’ sugar, vanilla, salt, and brown butter. Beat on low for 30 seconds and then switch to high speed and beat until creamy and smooth, about 1 minute. If the frosting is too thick, add a tablespoon of milk. If the frosting is too sweet, add 1/4 teaspoon salt.
4. Spread the frosting over the cooled cake. Start by making one thin layer over the cake to trap all the crumbs, then continue spreading the rest of the frosting over the top. Slice and serve.