Line a 9”x13” pan with parchment paper.
In a medium saucepan with attached candy thermometer, add butter, sugar, water, salt, and vanilla extract. Heat on medium high, stirring constantly as the butter is melted and the ingredients are combined.
Bring to a boil. Continue boiling and stirring gently until candy thermometer reads 298 degrees F.
Remove from heat and pour into the prepared pan. Spread evenly with a spatula. Cool completely.
For toffee bits: By hand, break toffee into small chunks and place in large zip lock bag. Seal bag and place on cutting board. Use a hammer to break the toffee chunks into small baking bits. Store extra bits in an air-tight container.
Wrap pairs of cookies, with bottoms together, in plastic wrap. Then store in an air-tight container or zip lock bag.