Preheat oven to 350 degrees F. Place liners in muffin pan.
In a mixer bowl (or large bowl), add butter and sugar. Cream together then add vanilla, eggs, and pumpkin. Once well mixed together then add in dry ingredients slowly. One the batter is smooth then it's ready.
Using a large ice cream scoop, scoop in batter into each liner.
In a small bowl, add in sugar, flour, cinnamon, and butter. Toss well with a fork to make the streusel topping.
Place some of the topping onto each muffin top.
Bake at 350 degrees F for 25 minutes.
Let muffins cool completely. Mix powdered sugar and water in a bowl until you get a nice thick but runny icing. Drizzle the muffin tops by using a spoon to go back and forth over the top.