Line a baking sheet with parchment paper or a silicone baking mat. Have your chopped almonds ready in a bowl, and measure out all ingredients before you start.
Place the butter, granulated sugar, water, and light corn syrup into your heavy-bottomed saucepan over medium heat. Stir gently as the butter melts and sugar dissolves. Avoid stirring too vigorously once it starts boiling to prevent crystallization.
Attach your candy thermometer to the saucepan, making sure it doesn’t touch the bottom. Let the mixture boil without stirring until it reaches 300°F (150°C), known as the hard crack stage. This usually takes about 10-15 minutes. The mixture will turn a deep amber color.
Once the toffee reaches 300°F, remove the pan from heat immediately. Stir in the vanilla extract and salt carefully. The mixture will bubble up slightly; that’s normal. Pour the hot toffee onto your prepared baking sheet and spread it evenly with a spatula.
Sprinkle the chocolate chips evenly over the hot toffee. Let them sit for a minute or two until they melt, then use an offset spatula or the back of a spoon to spread the melted chocolate into an even layer. Immediately sprinkle the finely chopped almonds over the top, gently pressing them into the chocolate to adhere.
Allow the toffee to cool at room temperature for at least 2 hours or until fully set and firm. Once hardened, break into irregular pieces or cut into squares as you prefer. Store in an airtight container to keep the crunch fresh.