Line a 9x13-inch baking sheet with parchment paper and butter it lightly. Sprinkle half the chopped almonds evenly over the parchment.
In a heavy-bottomed saucepan, combine butter, sugar, water, and corn syrup. Cook over medium heat, stirring constantly, until butter melts.
Once mixture begins boiling, stop stirring and attach a candy thermometer to the pan. Continue cooking until temperature reaches 290°F (hard crack stage), about 12-15 minutes.
Remove from heat immediately and stir in vanilla extract (it will bubble up).
Quickly pour hot toffee over almonds on prepared baking sheet, spreading evenly with a buttered spatula.
Let cool for 2-3 minutes, then sprinkle chocolate chips over hot toffee. Wait 2 minutes for chips to soften, then spread melted chocolate evenly over toffee.
Sprinkle remaining almonds over chocolate and press gently. Refrigerate for 1 hour until completely set.
Break into irregular pieces and store in an airtight container at room temperature for up to 2 weeks.