01 - Line a rimmed baking sheet with parchment paper or a silicone baking mat. Set aside.
02 - Place raw pecan halves in a dry skillet over medium heat. Toast for 3 to 4 minutes, stirring frequently, until fragrant and lightly browned. Transfer to a cutting board, let cool briefly, then roughly chop. Set aside.
03 - Combine granulated sugar, light corn syrup, and water in a large heavy-bottomed saucepan. Stir continuously over medium heat until the sugar fully dissolves and the mixture is smooth.
04 - Bring the syrup to a simmer and attach a candy thermometer to the side of the pan. Stop stirring and allow the mixture to cook undisturbed until it reaches 300°F (hard crack stage), approximately 10 to 12 minutes. Watch carefully to prevent scorching.
05 - Remove the saucepan from heat. Immediately add the unsalted butter, vanilla extract, flaky sea salt, baking soda, chopped toasted pecans, and puffed quinoa. Stir quickly and thoroughly with a heatproof spatula—the mixture will bubble and foam as the baking soda reacts.
06 - Pour the hot mixture onto the prepared baking sheet without delay. Use a spatula to spread it into an even layer approximately ¼ inch thick, working quickly before it begins to set.
07 - Sprinkle additional flaky sea salt over the surface while the brittle is still warm and pliable. Allow to cool at room temperature for at least 30 minutes, or until completely firm and hardened.
08 - Once fully set, break the brittle into irregular pieces by hand or tap gently with a knife handle. Transfer to a serving plate or store immediately.