In a large saucepan combine the butter, sugar, and salt. Stir over medium heat until the sugar has completely melted and mixture boils. Clip a candy thermometer to the pan and continue stirring over medium heat until mixture reaches 290 degrees F, about 15 minutes. Remove from heat and stir in vanilla.
Pour the toffee into the prepared pan, tipping pan to evenly spread. Allow to cool on a wire rack. In a small saucepan melt the white baking chocolate with the shortening. Spread the melted chocolate over the toffee and sprinkle with almonds. Chill at least 30 minutes or until chocolate is set. Break into pieces.