Place the salt block in the refrigerator and chill for at least an hour. Once the block is totally cold, spray it with nonstick cooking spray and set it aside as you make your caramel.
Place the sugar in a medium saucepot and set over medium-high heat. Let the sugar melt completely and become a deep amber color, 8 to 10 minutes.
Once the sugar is caramel in color, add in the corn syrup and baking soda. At this point, the mixture will bubble up the sides of the pot, so use caution and keep stirring. Immediately add the nuts and then pour the mixture onto the salt block. Let it cool and set completely.
Once cool, the brittle can be lifted with a spatula and broken into pieces.