Combine brown sugar, granulated sugar, 1 teaspoon pumpkin pie spice, and instant pectin in a medium bowl. Stir in pumpkin puree until well combined. Refrigerate until ready to use.
Place one sheet of puff pastry onto a lightly floured, movable, flat surface, such as a lightweight cutting board. Lightly dust surface of pastry with flour and roll lightly just to smooth creases.
Spread with 1/3 cup of pumpkin mixture, stopping 1/4-inch from edges.
Roll a second sheet of puff pastry on a lightly floured surface to smooth creases; place on top of the first sheet and press down gently. Repeat the process two more times with remaining pastry sheets and remaining filling. Refrigerate filled pastry for 15 minutes.
Preheat oven to 400°F. Line a baking sheet with parchment paper or a nonstick silicone mat.
Working with one filled pastry at a time, cut into 1 1/2-inch strips.
Place strips on baking sheet spacing about 1/2-inch apart. Carefully lift strips and twist each 3 times before laying down. (Leave remaining filled pastry in refrigerator until ready to bake.)
Mix together coarse sugar and remaining 1 tablespoon pumpkin spice.
Beat egg and milk together in a small bowl. Using a pastry brush, brush each twist with egg wash and evenly sprinkle evenly with coarse sugar mixture.
Bake 22 to 24 minutes, or until puffed and golden brown. Cool on baking sheet 5 minutes, then transfer to a wire rack to cool completely.
Repeat process two more times, cutting and baking one remaining filled pastry at a time.
To make pumpkin pie spice at home, combine 2 tablespoons of ground cinnamon, 2 teaspoons of ground nutmeg, 2 teaspoons of ground ginger, and 1 teaspoon of ground allspice.
Sanding sugar is larger, polished grains of sugar – about four times larger than those in granulated sugar. Because the sugar crystal grains are large and reflect light, they give off a “sparkling” effect. The large-grained sugar won’t melt and disappear as it bakes, giving a nice crunch to the dessert topping.