Cover a large baking sheet with aluminum foil or parchment paper.

In a medium to large heavy bottomed saucepan, combine the butter, sugar and salt over low heat until butter is melted, whisking constantly. Bring to a steady (not rolling) boil over medium to medium-high heat, and cook, whisking constantly, until the mixture has reached 285 to 300 degrees F (137 to 150 degrees C).

Remove toffee from heat and stir in vanilla. Pour mixture onto the prepared baking sheet. (If desired, you can sprinkle some of the nuts on the baking sheet before pouring on the toffee).

Sprinkle the chocolate chips over the top, and let chocolate soften for a few minutes. Spread the chocolate into a thin even layer. Sprinkle with chopped almonds.

Refrigerate until set. Break into pieces, and store in an airtight container.