Preheat oven to 350°F or 176℃. Line a 9x9-inch baking dish with parchment paper.
In a medium bowl, whisk together the flour, cinnamon, pumpkin pie spice, salt, and baking powder.
In a separate large bowl, cream together the softened butter and brown sugar until fluffy.
Add the egg, vanilla, maple syrup, pumpkin puree, and milk. Stir until smooth.
Gradually mix in the dry ingredients just until combined—don’t overmix.
Pour the batter into the prepared pan and smooth the top with a spatula.
Make the streusel: In a small bowl, combine the flour, cinnamon, and brown sugar. Cut in the cold cubed butter using a pastry cutter or your fingers until it resembles coarse crumbs. Sprinkle evenly over the batter.
Bake for 27–32 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Let cool in the pan for 10 minutes before adding glaze.
Make the glaze: Whisk together powdered sugar, melted butter, milk, and vanilla until smooth. Drizzle over warm cake.
Slice, serve, and enjoy