01 - Line a rimmed baking sheet with parchment paper or a silicone baking mat and set aside.
02 - Toast pecan halves in a dry skillet over medium heat for 3 to 4 minutes, stirring frequently, until fragrant and lightly golden. Allow to cool, then roughly chop and set aside.
03 - In a large heavy-bottomed saucepan, combine the granulated sugar, light corn syrup, and water. Stir continuously over medium heat until the sugar has fully dissolved.
04 - Bring the syrup to a simmer and attach a candy thermometer to the side of the pan. Stop stirring and cook until the mixture reaches 300°F (hard crack stage), approximately 10 to 12 minutes.
05 - Remove the saucepan from heat. Immediately add the unsalted butter, vanilla extract, sea salt, baking soda, chopped pecans, and puffed quinoa. Stir quickly and thoroughly to combine; the mixture will foam and bubble rapidly.
06 - Immediately pour the hot mixture onto the prepared baking sheet. Using a heatproof spatula, spread it evenly to approximately ¼-inch thickness, working quickly before it begins to set.
07 - Sprinkle the surface generously with additional flaky sea salt while still hot. Allow the brittle to cool completely at room temperature for at least 30 minutes until fully hardened and set.
08 - Once fully cooled and hardened, break the brittle into 12 irregular pieces by hand or tap gently with the handle of a knife. Transfer to a serving plate or store immediately.