For the cinnamon swirl:
- In a small bowl, mix the melted butter, sugar, and cinnamon until a thick paste forms. Set aside.
For the streusel topping:
- In a small bowl, mix the flour, sugar, cinnamon, and melted butter until crumbly. Set aside.
For the cake:
- Preheat oven to 350 degrees F. and line an 8x8 square baking dish with parchment paper. Set aside.
- In a small saucepan over medium heat, melt the butter and continue cooking until it begins to foam and brown. Set aside.
- In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
- 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.
- Divide half of the cake batter into the prepared baking dish.
- Swirl half of the cinnamon swirl paste through the batter.
- Top with the remaining cake batter and repeat the process of swirling the cinnamon paste through the top layer.
- 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.
- Remove from the oven and transfer the cake to a wire rack. Let cool to room temperature.
- In a small bowl, whisk the ingredients for the icing. Drizzle over the cake and serve.