Combine the sugar, brown sugar, flour, cinnamon, and butter in a small mixing bowl with a fork until everything is combined and it forms a crumbly mixture. Set Aside.
Combine flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg, brown sugar, granulated sugar, pumpkin puree, vegetable oil, sour cream, and beaten egg. Beat on low until smooth and combined.
Spread the coffee cake batter into the prepared cake pan. Place on a small baking sheet.
Sprinkle the streusel topping evenly over the batter. Bake about 50 – 60 minutes at 375 degrees F. or until a toothpick inserted in the center comes out clean.
Allow the cake to cool for 20 minutes.
Loosen the edges of the cake from the pan with a knife and transfer to a plate.
Combine the powdered sugar, milk, and vanilla in a small bowl until mixed well. Add more milk if it is too thick to drizzle.