01 -
Line a rimmed baking sheet with parchment paper. Measure the almonds, butter, baking soda, and flaky salt into small bowls so they are ready. Once the caramel hits temperature you will not have time to measure.
02 -
Stir sugar, corn syrup, water, and fine salt together in a heavy 2-quart saucepan over medium heat until the sugar disappears. Clip on a candy thermometer and stop stirring. Let it boil until it reaches 300°F (150°C), the hard crack stage. This takes 8-12 minutes.
03 -
As soon as the thermometer hits 300°F, pull the pan off the heat. Stir in the almonds and butter. The butter melts instantly and the almonds get coated in bubbling amber syrup. Work fast.
04 -
Add the baking soda and stir vigorously for about five seconds. The mixture will foam up and turn pale. This reaction is what creates the brittle texture.
05 -
Scrape the mixture onto the prepared sheet. Use an offset spatula or two forks to push it into a thin, even layer. Sprinkle the flaky salt over the surface immediately so it adheres.
06 -
Let the brittle sit at room temperature until it is completely hard, about 1 hour. Lift the sheet of candy off the parchment and break it into irregular shards with your hands.