Preheat oven to 400°F (200°C) and line large baking sheet with parchment paper.
Arrange Saltine crackers in single layer on prepared baking sheet, fitting tightly together.
In medium heavy-bottomed saucepan over medium heat, melt butter. Stir in brown sugar, vanilla, and salt. Boil for exactly 3 minutes until mixture reaches 240-250°F and deep amber color.
Carefully pour hot toffee over crackers, ensuring even coverage. Work quickly as it sets fast.
Bake 5-7 minutes until toffee is actively bubbling across surface.
Mix granulated sugar and cinnamon. Immediately sprinkle over hot toffee when removed from oven.
If using chocolate, wait 10 minutes then drizzle melted chocolate while toffee is still warm. Add nuts while chocolate is soft.
Cool completely for 25-30 minutes until firm and no longer warm, then break into pieces.
Notes
Watch toffee carefully during 3-minute boil to prevent burning. Use candy thermometer for precision (240-250°F).
Safety warning: Caramel reaches over 300°F – use extreme caution when pouring.
If toffee crystallizes, add 1 tablespoon water and reheat gently while stirring.
Store in airtight container up to 1 week at room temperature, 2 weeks refrigerated, or 3 months frozen.