Line a 9x13-inch baking sheet with parchment; sprinkle half the almonds evenly over bottom.
Combine butter, sugar, water, and corn syrup in a heavy-bottomed saucepan; cook over medium, stirring constantly, to 300°F on a candy thermometer (hard crack).
Off heat, quickly stir in vanilla; immediately pour hot toffee over almonds and spread evenly with a spatula.
Sprinkle chips over hot toffee; stand 2-3 minutes to soften, then spread chocolate evenly.
Sprinkle with remaining almonds; press gently to adhere.
Refrigerate 1 hour until completely set; break into irregular pieces and store airtight.