Make Toffee

1. Prepare a cookie sheet by lining with silicone baking mat or foil. If using foil, coat with nonstick spray and wipe with paper towel
2. In a large saucepan, add water then sugar, assuring that all sugar is soaked and the mixture resembles wet sand. Add salt, corn syrup and butter
3. Clip a candy thermometer to the side of the pan, making sure the bulb is submerged. Bring this mixture up to a boil over high heat 
4. Once boiling, reduce heat to medium to prevent boiling over. Cook, whisking every 2 minutes or so, until the mixture reaches 300° (hard crack stage) 
5. Turn the heat off and carefully pour in the vanilla extract (it will bubble and splatter). Stir to combine, then add sliced almonds 
6. Pour the mixture onto the prepared pan and spread to the edges with a spatula, working quickly
7. Let cool completely, about 20-30 minutes

Temper Chocolate

1. Remove and set aside about ⅓ of your dark chocolate
2. Melt the larger amount of chocolate over a double boiler
3. Clip a thermometer to the side of the pot and heat until the chocolate is at 120°, stirring frequently
4. Remove from the heat and slowly add pieces of the reserved chocolate (the "seed"), stirring until each piece is melted before adding more. Add chocolate pieces only until the melted chocolate has cooled to 85º - 90°
5. Remove any unmelted pieces of chocolate

Layer Toffee & Chocolate

1. Spread the tempered chocolate over the cooled, hardened toffee with a small offset spatula
2. Allow to sit at room temperature until it sets completely, about 5 minutes
3. To break into pieces, peel the entire sheet of toffee from the silicone mat or foil and place on the cookie sheet, chocolate-side-down 
4. Tap the toffee with a wooden spoon in several places to break into shards This method will prevent the chocolate from coming away from the toffee and not leave fingerprints on the chocolate