Line a large cookie sheet with a silicone liner or buttered parchment paper. Set aside.
In a large heavy pan, heat the butter, sugar, water, corn syrup, salt, and vanilla over medium heat. Bring to a boil.
Continue cooking till mixture reaches about 290 degrees and turns a deep caramel color. (Right between the soft and hard crack stage.) Watch carefully, it can burn quickly after it reaches 280°.
Quickly pour the hot mixture onto the pan. Let it sit for about 3-5 minutes, then sprinkle the chocolate chips evenly over the top.
Let sit for 5-10 minutes or till chocolate is melted. Spread the chocolate over the top, then sprinkle with chopped almonds.
Let toffee cool completely, then break into pieces.
Notes
You can use a candy thermometer, or drop a spoonful of the hot mixture into a cup of cold water. If it cracks, it's ready.
I've tried the recipe without the corn syrup. It still works, but it's trickier at the end because it tends to separate, so you have to stir very vigorously.
Yield is about 1 1/2 pounds of toffee; nutritional information is just an estimate.