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.