1/2 cup corn syrup
1/2 cup water
1 tsp kosher salt
1/2 cup butter, cubed
2 cups toasted pistachios, chopped
1/2 tsp baking soda
1/2 tsp vanilla
Toast pistachios on baking sheet in 300 degree oven for 5-7 minutes, until fragrant. Remove from oven and sprinkle with kosher salt.
Butter the bottom of a large baking sheet. Set aside.
Stir sugar, syrup, water and salt together in heavy-bottom pan over medium heat. Using candy thermometer, bring sugar mixture to 240 degrees (soft ball stage), stirring frequently. Stir in butter and pistachios, and bring to 280 degrees (soft crack stage).
Remove from heat and quickly stir in baking soda and vanilla, just until mixed through. Immediately pour onto buttered baking sheet and spread out to desired thickness. Just before candy hardens (30 seconds or so), sprinkle kosher salt lightly across the top. Let cool and break into bite-sized chunks.
Keeps for up to 2 weeks in an airtight container.