Preheat the oven to 350°. Spray or oil a large baking sheet or roasting pan. Pour in crackers and cashews.
In a heavy sauce pot over medium heat, combine butter, sugar, syrup and salt. Stir constantly while bringing it to a boil. When a rapid boil happens, allow it to boil without stirring for 5 minutes. Remove from heat and mix in baking soda and vanilla. Carefully pour over the crackers and cashews and mix well. Bake for 20 minutes, stirring once after 10 minutes.
Remove from oven and allow to cool completely before serving. Stove in an airtight container for up to 4 days!