In a medium skillet over medium heat, melt butter. Add pumpkin pie spice and cook, stirring, until fragrant, about 30 seconds. Add milk, cream cheese, and pumpkin puree and cook, stirring constantly, until thickened, about 5 minutes. Stir in crackers and white chips until melted and smooth. Cook, stirring, until mixture releases from sides and bottom of pan, 8 to 10 minutes.

Grease a quarter sheet pan with cooking spray. Transfer pumpkin mixture to pan and spread in an even layer. Let cool to room temperature, then refrigerate until set, at least 2 hours and up to overnight.

Place orange sanding sugar in a small bowl. Spray your hands with cooking spray to prevent sticking. Roll cheesecake mixture into 1 1/2" balls. Roll balls in sanding sugar until coated.

Using a toothpick, press ridges into sides of balls (to resemble pumpkins). Place a dark chip on top. Refrigerate until cold, at least 1 hour, or store in an airtight container up to 5 days.