Line a cookie sheet with a piece of parchment paper; set aside. Spray a wooden spoon with non-stick cooking spray; set aside.
In a large, heavy saucepan, combine the sugar, corn syrup, butter, cinnamon, cardamom and nutmeg. Split the vanilla bean in half and scrape the seeds into the pan as well. Discard the bean.
Place the pan over low heat and stir until the sugar is dissolved. Stop stirring and let the mixture come to a boil (still over low heat) and cook until the mixture reaches 330 degrees F on a candy (or instant-read) thermometer.
Remove from the heat and use the oiled spoon to quickly stir in the pumpkin seeds.
Quickly and carefully pour the mixture out onto the prepared baking sheet. Spread it out as much as possible. Let cool completely and then break into pieces. The brittle can be stored in an airtight container at room temperature for up to 1 month.