Preheat oven to 300 degrees.  Line a large baking sheet with parchment paper.  Spread the almonds on the sheet and bake for 15 minutes.

Remove almonds from oven and allow to cool.  Set one cup of whole almonds aside and chop up the rest.  The chopped almonds will go on top of the chocolate on both sides of the toffee.

Line a 12x17 jelly roll pan with parchment paper and set aside.

In a heavy duty saucepan, melt the cubed butter over medium heat.  Stir occasionally with a wooden spoon as it melts.  Once melted, add the water, sugar, salt and corn syrup.  Stir constantly until the sugar dissolves, then brush down the sides of the pan with a water moistened pastry brush.  Attach a candy thermometer to the pan (do not let it touch bottom of pan or you will have an inaccurate temperature reading).

Stir occasionally as you bring the mixture to a boil.  Once boiling, you can stop stirring.  Around 235 degrees F, rapid bubbles, a thicker consistency as well as a slightly darker color forms.  At the 265 degrees F point (hard ball stage), stir in the 1 cup of whole toasted almonds.  This is the point that the mixture might separate.  If this occurs, remove the candy thermometer and give the mixture a strong solid stir incorporating the almonds.  Replace thermometer back on pan.  Cook and stir the candy until it reaches 290 degrees (soft crack stage).

Turn off the stove, remove the pan from the heat and pour toffee out onto the prepared jelly roll pan.  Smooth toffee into an even layer.  Toffee should be thick and not spread to edges.  Let toffee cool for 5 minutes, than add half of the dark chocolate melts on top.  Let chocolate soften and melt from the heat of the toffee, then spread the melted chocolate into a thin, even layer. 

Sprinkle half of the crushed almonds onto the wet chocolate and press down gently with the back of a spatula to adhere them.  Refrigerate for 20 minutes to set chocolate.

Once set, flip the toffee over carefully.  Melt the remaining chocolate melts in microwave and spread on toffee.  Press chopped almonds on top of chocolate and refrigerate for 20 minutes.

Once set, you can break toffee up with your hands into whatever size you deem best for your toffee.  Enjoy!