Preheat oven to 350 degrees F. Line baking sheet with parchment paper and set aside. Arrange pumpkin seeds on baking sheet in an even layer and roast for 10 minutes. Remove from oven to cool.

In small pot on medium-high heat, bring maple syrup and sugar to boil (do not stir). Use candy thermometer – once it reaches 300 degrees F or “hard crack stage*” add butter, pumpkin pie spice, salt, vanilla, baking soda and 1 ¼ cups pumpkin seeds.

Quickly transfer mixture to prepared baking sheet. Spread into an even layer and top with remaining pumpkin seeds. Allow brittle to cool completely, about 30 minutes, before breaking into pieces.