Prepare the Baking Sheet: Begin by lining a 9x13 inch baking sheet with parchment paper. Ensure there is some overhang on the sides; this will make it easier to lift the toffee out once it has set.
Cook the Butter Mixture: In a medium saucepan, combine the cubed unsalted butter, granulated sugar, water, and salt. Place it over medium heat, stirring continuously until the butter has completely melted and the sugar has fully dissolved into a uniform mixture.
Bring to a Boil: Raise the heat slightly to bring your mixture to a boil. Remember to keep stirring constantly. Use a candy thermometer to monitor the temperature; you want to cook the mixture until it reaches the hard crack stage (300°F or 150°C). This should take approximately 10-15 minutes.
Incorporate Vanilla: When your toffee mixture reaches the desired temperature, carefully remove the saucepan from the heat. Stir in the vanilla extract, being cautious of any steam.
Spread on the Baking Sheet: Immediately pour the hot toffee mixture onto the lined baking sheet. Using a spatula, spread the toffee into an even layer, working quickly as it will begin to set.
Top with Chocolate Chips: Sprinkle the semi-sweet chocolate chips evenly over the hot toffee surface. Let them sit undisturbed for about 2-3 minutes, allowing the chocolate to soften. Then, use a spatula to spread the melted chocolate across the toffee.
Add Pecan Topping: Generously sprinkle the chopped pecans over the melted chocolate layer, gently pressing them down to ensure they adhere.
Finish with Sea Salt: For a delightful contrast, lightly sprinkle sea salt over the top of the pecans and chocolate. This will enhance the flavor profile of the toffee.
Cool and Set: Allow the toffee to cool at room temperature for about 1 hour until it is firm. For easier handling, place it in the refrigerator for an additional 30 minutes to ensure it fully sets.
Break and Serve: Once the toffee has set, lift it out of the baking sheet using the parchment overhang. Break it into pieces as desired and serve immediately or store in an airtight container for later enjoyment.
Notes
For best results, use a candy thermometer to ensure the toffee reaches the hard crack stage.