Prepare a baking sheet by lining it with parchment paper.
In a saucepan, melt the butter over medium heat.
Add sugar, water, and salt to the melted butter.
Stir continuously until the mixture comes to a boil.
Reduce heat to medium-low and cook for about 10-15 minutes, stirring frequently.
Use a candy thermometer to monitor the temperature; aim for 300°F (hard crack stage).
Remove from heat and stir in vanilla extract.
Quickly pour the mixture onto the prepared baking sheet.
Let the toffee cool slightly before sprinkling chocolate chips on top.
Once the chocolate is melted, spread it evenly and sprinkle with nuts if desired.
Allow to cool completely, then break into pieces and enjoy!