Silpat mats or parchment paper should be used to line a big baking sheet with a rim (or spray with nonstick spray).

In a large saucepan, combine the butter, water, corn syrup, and sugar. Prepare the cashews and baking soda by measuring them out.

For about 10 minutes, cook the mixture in the saucepan, stirring regularly, until it turns golden brown and registers 300°F on a candy thermometer.

Add the baking soda right away after taking the pan off the heat. It will vigorously bubble up. Pour quickly onto your baking sheet and spread into an even layer with a silicone spatula or long wooden or metal spoon. Quickly whisk in the vanilla extract and cashews. (For the first minute or two, you can really push it down; however, use caution because it is HOT.)

Sea salt should be added on top. After allowing it to cool for about 30 minutes, cut it into pieces. Use an airtight container for storage.