Combine first 3 ingredients in a small, heavy saucepan over medium-high heat, stirring just until combined; bring to a boil. Cook, without stirring, until a candy thermometer registers 325 or until syrup begins to caramelize. Stir in vanilla and salt. Working carefully and quickly, pour sugar mixture onto a baking sheet covered with parchment paper; spread to desired thickness.
Let toffee stand 5 minutes.
Sprinkle chocolate over warm toffee; let stand 5 minutes.
Spread melted chocolate in a thin, even layer over toffee; immediately sprinkle with chopped almonds.
Let stand 1 hour or until completely cool. Break toffee into pieces.
