Preheat oven to 325°F (170°C).

For batter: In a large bowl, whisk together pumpkin, brown sugar, granulated sugar, sour cream, oil, eggs, melted butter, and vanilla bean paste.

In a medium bowl, whisk together flour, baking powder, salt, nutmeg, pie spice, cinnamon, and baking soda. Gradually whisk flour mixture into pumpkin mixture until smooth and well combined.

Spray a 10-cup Bundt pan with baking spray with flour. Spoon batter into prepared pan. Tap pan on a kitchen towel-lined counter several times to settle batter and release any air bubbles.

Bake until a wooden pick inserted near center comes out clean and an instant-read thermometer inserted near center registers 200°F (93°C) to 205°F (96°C), 1 hour to 1 hour and 15 minutes. Let cool in pan for 15 minutes. Invert cake onto a wire rack, and let cool completely.

For topping: In a small bowl, stir together granulated sugar, brown sugar, cinnamon, and nutmeg. Brush cake lightly with melted butter; cover with sugar mixture, pressing gently to help adhere, if needed. Serve immediately.