Melt the butter over low heat in a heavy-bottomed pot. Prep a sheet pan with melted butter and set aside.
Add the sugar and salt to the melted butter.
Simmer over medium heat until it reaches 285-290°F, reducing heat if necessary to prevent boiling too rapidly. If it's snapping and popping the heat is too high.
Once at temperature, turn off the heat, add the vanilla and mix well.
Pour the mixture out onto the greased pan in ribbons. Let cool for 10-15 minutes or until the pan is warm to the touch.
Top with chocolate evenly. Let it melt.
Spread the melted chocolate and top with the chopped nuts.
Cool overnight, cover airtight to prevent moisture from getting in. Humidity can make the toffee sticky and harder to chew.
