Line a jelly roll pan with parchment paper or with a silicone baking mat.
Sprinkle the chopped almonds over the bottom of the prepared pan. They won’t cover the surface of the pan. Set aside.
Add the butter and sugar to a large, heavy saucepan.
Melt the butter over low heat, stirring regularly.
Once the butter has melted, increase the heat to medium-low, and bring the butter mixture to a boil. Occasionally gently stir the toffee mixture.
Cook until the toffee mixture is 295-300 degrees F (hard crack stage). The toffee mixture should be rich amber brown (check out the pictures above the recipe for reference).
Carefully pour the toffee mixture over the nuts in the prepared pan. Use a silicone spatula to spread out the toffee as needed.
Sprinkle the chocolate chips over the top.
Let the chocolate chips stand for about 5 minutes to begin to melt.
Carefully spread the melted chocolate chips over the top of the toffee with an offset spatula, and sprinkle with the chopped nuts, if using.
Let the toffee sit until it has set.
Break into pieces to serve.
Notes
Almonds: I use unsalted almonds to better control how salty the toffee is.
Salted butter: I like to use salted butter in this recipe. If you're using unsalted butter, you'll need to add 1 teaspoon of salt along with the butter and sugar.
Sugar: You'll need granulated sugar (white sugar) for this recipe.
Semi-sweet chocolate chips: You can use dark chocolate chips or milk chocolate chips if you prefer. The chocolate layer is fairly thin, so if you like a thick layer of chocolate on your toffee, increase the amount of chocolate chips.