Line a 12x17 baking sheet with parchment. Place it on top of hot pads where it can rest undisturbed for 3-5 hours. The baking sheet will get very hot when the toffee is poured onto it.
Pulse 1/4 cup of slivered almonds in a food processor or finely chop by hand. Set aside.
Bring 1/4 cup water, sugar, and corn syrup to a boil over medium heat.
1/4 cup water, 1 1/2 cups sugar, 1/2 cup corn syrup
Add the butter, stirring gently. When it has melted, add the almonds.
1/2 pound butter, 1 pound almonds {blanched and sliced}
Stir constantly until the toffee/buttercrunch has browned and it smells like caramel (~15 minutes. Be patient, it's a slow process.). The mixture will be very thick but keep stirring! If you're using a candy thermometer, it will be ready at 295 degrees (hardcrack stage).
Remove from heat and using a wooden spoon, very quickly pour toffee/buttercrunch onto the baking sheet lined with parchment, and spread it around as evenly as possible. Work quickly because it becomes hard to spread as it cools.
Sprinkle the toffee/buttercrunch with the chocolate chips, and allow them to get melty. Pro tip: If your kitchen is cold, lightly tent a piece of foil over the baking sheet to assist the melting process of the chocolate chips.
12 oz semi-sweet chocolate
Once the chocolate chips are shiny, use an offset spatula or butter knife to spread the chocolate evenly over the toffee.
Immediately sprinkle with reserved crushed almonds.
Place the tray in a cool place in your house and allow to cool completely. It can take up to 5 hours to cool completely. It has cooled when the chocolate on top is no longer shiny.
Break into pieces and store in an air-tight container at room temperature for up to 4 weeks.
Notes
There are no substitutes for the corn syrup in this recipe. In order to for your almond buttercrunch to turn out, you must use corn syrup.
Important: for best results, make your homemade almond roca on a cool dry day. Additional humidity in the air can and likely will impact the quality of your toffee.
To avoid the toffee separating, keep the temperature constant and avoid cooking the buttercrunch too quickly.
If you don't have a candy thermometer, the toffee will be ready when it is a creamy beige color and it will smell like caramel. You'll be able to move a wooden spoon through it and the toffee will stay separated for a few seconds. See photos in the post above for a visual of what the finished toffee should look like.