Preheat oven to 350°F and grease a muffin tin (or line with muffin liners).
In the bowl of a stand mixer, mix together the butter, oil, sugar and brown sugar until well-combined.
Mix in the egg, vanilla, pumpkin and milk.
Add the flour, salt, soda, baking powder and pumpkin pie spice. Stir until just combined.
Fill 18 muffin cups about ⅔ full each; set aside.
Combine the streusel ingredients in a bowl and sprinkle evenly over the muffin batter.
Bake for 20-22 minutes, or until a toothpick pressed into the center of the middle muffin comes out mostly clean. (A few moist crumbs are fine).
In a small bowl, combine the icing ingredients and drizzle over the muffins.