Butter a large baking sheet pan and set to the side.
In a large sauce pan, combine the sugar, water, butter and corn syrup. Bring to a boil.
Cook over medium high heat, stirring occasionally, until mixture is light brown and registers 300 degrees on a candy thermometer, about 20 minutes.
Remove from heat and stir in the baking soda; mixture will bubble.
Stir in the nuts and immediately scrape the brittle onto the prepared pan. Use the back of a greased spoon or spatula to spread into a thin layer. Sprinkle with sea salt.
Let cool completely, about 30 minutes, then break into large pieces. Store in an airtight container for up to 1 month.