Make streusel- in a bowl, melt the butter and let it cool for a few minutes. Mix in the sugar, flour, pumpkin pie spice, and cinnamon until combined. Place this in the fridge while making the rest of the cake.
8 tbsp unsalted butter, ¾ cup granulated sugar, 1 cup all-purpose flour spooned and leveled, 1 tsp pumpkin pie spice, ½ tsp cinnamon
Preheat oven to 350 F and grease an 8x8 square pan. Line with parchment paper for easy removal. Set aside.
In a small bowl, mix together the flour, baking powder, salt, and pumpkin pie spice.
2 cups all-purpose flour, 2 tsp baking powder, ½ tsp salt, 2 tsp pumpkin pie spice
In a separate large bowl, use an electric mixer to cream sugar and butter together until smooth, about 1-2 minutes. Add the egg, sour cream, vanilla extract, and pumpkin puree, mixing until combined.
¼ cup unsalted butter, ¾ cup granulated sugar, 1 large egg, ¼ cup sour cream, ½ cup pumpkin puree, 2 tsp vanilla extract
Add the flour mixture and milk in alternating additions, starting and ending with the flour mixture. Mix until just combined, be careful not to overmix here.
¼ cup whole milk
Pour half the batter in the greased pan. Sprinkle a little less than half of streusel on top of the batter. Carefully spread the rest of the batter on top. Finally, top evenly with the remaining streusel.
Bake for 30-35 minutes, or until a toothpick comes out clean. Allow the cake to cool in the pan for 10-15 minutes.
Once cooled, top with pumpkin icing- in a small bowl whisk together the powdered sugar, pumpkin pie spice, and milk until smooth. Drizzle the sugar glaze over the cake, slice, and enjoy.
½ cup powdered sugar, 1 ½ teaspoons milk, ⅛ tsp pumpkin pie spice