Preheat your oven to 425°F (215°C). In a small bowl, mix together all purpose flour, granulated sugar, brown sugar, and melted unsalted butter until the mixture looks crumbly. Place the bowl in the refrigerator until ready to use.

In a large bowl, whisk pumpkin purée, oil, granulated sugar, brown sugar, eggs, and vanilla extract until smooth and well combined.

Stir in the sour cream until fully incorporated.

Gently fold the flour, baking powder, pumpkin pie spice, and salt into the wet ingredients with a rubber spatula until no dry streaks of flour remain. Be careful not to overmix.

Place paper liners in every other cup of a 12-cup muffin pan. Divide the batter between the cups, filling each almost to the top. Sprinkle the chilled streusel generously over each muffin.

Bake the muffins at 425°F for 5 minutes, then reduce the temperature to 350°F (180°C). Continue baking for 15-18 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs attached.

Let the muffins cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

Whisk together powdered sugar, maple syrup, and heavy cream in a small bowl until smooth.

Drizzle the icing over cooled muffins and serve!