For the cinnamon swirl:

1. In a small bowl, mix the melted butter, sugar, and cinnamon until a thick paste forms. Set aside.

For the streusel topping:

1. In a small bowl, mix the flour, sugar, cinnamon, and melted butter until crumbly. Set aside.

For the cake:

1. Preheat oven to 350 degrees F. and line an 8x8 square baking dish with parchment paper. Set aside.
2. In a small saucepan over medium heat, melt the butter and continue cooking until it begins to foam and brown. Set aside.
3. In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
4. In a large bowl, whisk together sugars, pumpkin puree, vanilla, eggs, browned butter, cinnamon, and milk.  Add the dry ingredients and mix until everything is incorporated.
5. Divide half of the cake batter into the prepared baking dish.
6. Swirl half of the cinnamon swirl paste through the batter.
7. Top with the remaining cake batter and repeat the process of swirling the cinnamon paste through the top layer.
8. Top with the prepared streusel topping and bake for about 50 minutes or until your cake tester comes out clean. Bake time may depend on your oven range.
9. Remove from the oven and transfer the cake to a wire rack. Let cool to room temperature.
10. In a small bowl, whisk the ingredients for the icing. Drizzle over the cake and serve.