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 completely, then roughly chop into bite-size pieces.
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 and the mixture is smooth.
04 - Bring the mixture to a steady simmer and attach a candy thermometer to the side of the pan. Stop stirring and cook until the thermometer registers 300°F (hard crack stage), approximately 10 to 12 minutes.
05 - Remove the saucepan from heat. Immediately add the unsalted butter, vanilla extract, flaky sea salt, baking soda, chopped pecans, and puffed quinoa. Stir quickly and thoroughly to combine — the mixture will bubble and foam as the baking soda activates.
06 - Pour the hot mixture onto the prepared baking sheet without delay. Using a heatproof spatula, spread it out evenly to approximately 1/4-inch thickness, working quickly before it begins to set.
07 - Sprinkle the surface generously with additional flaky sea salt while still warm. Allow the brittle to cool undisturbed at room temperature for at least 30 minutes until fully hardened and set.
08 - Once completely cool and firm, break the brittle into 12 irregular pieces by hand or tap gently with the handle of a knife. Serve immediately or store for later enjoyment.