Grease a 9×12 or 9×9 metal baking dish, then line it with parchment paper, leaving an overhang for easy removal; do not grease the top side of the parchment paper.

Toast the almonds and chop them: either (a) heat whole almonds in a dry skillet over medium heat for 5–7 minutes, stirring every 30 seconds, or (b) roast almonds on a baking sheet at 325°F for 10–15 minutes. Let cool, coarsely chop, then spread half of the chopped almonds evenly in the prepared pan and reserve the remaining half for topping.

In a large heavy saucepan (3–4 quart minimum), combine 1 cup granulated sugar, 1/2 lb (2 sticks) unsalted butter, 1 tsp vanilla extract, and 1/2 tsp fine sea salt. Set the pan over medium heat. Stir constantly with a wooden spoon until the butter melts and the mixture comes to a boil.

Continue stirring constantly and cook the mixture until it turns a deep caramel color and reaches 300–310°F on a candy thermometer (hard‑crack stage). This usually takes about 8–10 minutes over medium heat. Be very careful—the mixture is extremely hot. Do not taste.

Immediately pour the hot toffee into the prepared pan over the layer of almonds. Tilt the pan to help the toffee spread evenly over the nuts; it does not have to reach the edges or be perfectly smooth.

While the toffee is still hot, sprinkle 1 cup semi‑sweet chocolate chips (or milk chocolate) evenly over the surface. Let sit 2 minutes so the chips soften and glisten, then use an offset spatula to spread the melted chocolate into an even layer.

Sprinkle the remaining chopped almonds over the melted chocolate and press them gently so they adhere.

Let the toffee cool at room temperature for at least 2 hours, or until the chocolate is fully set. Break or cut into pieces to serve. Store in an airtight container at room temperature for up to one week.