Preheat the oven to 350°F. Spray a 9×13-inch pan with nonstick cooking spray or line with parchment paper. For a thicker cake, use a 9×9-inch pan.
In a large bowl, combine the flour, sugar, baking powder, baking soda, pumpkin pie spice, cinnamon, and salt. Stir in the pumpkin, milk, and whisked egg until just combined. Pour into the pan and spread evenly.
Streusel crumb topping
In a small bowl, mix the flour, brown sugar, pumpkin spice, and butter with a fork until it resembles crumbles. You may need to use your hands to combine. Sprinkle over the top of the cake batter.
Bake 25 to 30 minutes, or until a toothpick inserted into the center comes clean. Let cool.
If making the glaze, stir together the powdered sugar, maple syrup, and milk in a small bowl. Drizzle over the top. Cover until ready to serve.
Notes
For pumpkin streusel muffins: Fill the liners about 2/3 the way full (I like to use a large cookie scoop). Then add about 1 Tablespoon of the crumb topping to each muffin. Bake the muffins at 375°F for about 18 to 20 minutes, or until a toothpick inserted into the center comes out clean. Be careful not to brown the tops too much. Makes about 16 muffins.Storage: Store leftovers in a covered container up to 3 days. Freeze up to 3 months.