Step 1

This recipe works best when you prep everything first. Line a 15″ x 10″ rimmed pan with foil, extending over the edges. Butter the sides of a heavy-bottomed 2-quart sauce pan with the 1/2 teaspoon of butter. And measure out all ingredients.

Step 2

Place sauce pan over medium heat and melt remaining 1-1/2 cups butter. Then stir in sugar, corn syrup, and water with a wooden spoon. Nudge the heat up just a bit (nearly medium-high) and stir fairly constantly, until mixture comes to a boil.

Step 3

Clip candy thermometer to the inside of the sauce pan. Stir only occasionally and briefly with a wooden spoon, slowly and evenly, until candy thermometer reaches 305° F - this should take about 15 to 17 minutes. The mixture will change color as it cooks, from very light to deep amber. Watch carefully, especially near the end, as the temperature rises at a faster rate right at the end. Immediately remove sauce pan from heat.

Step 4

Pour hot liquid toffee mixture into foil-lined pan. Allow to sit until mixture is stable, but still hot - this should take 2 to 3 minutes.

Step 5

Quickly sprinkle mini chocolate chips over the top of the hot toffee, in an even layer. Cover pan with foil to seal in heat and melt the chocolate chips. Let sit for 3 minutes undisturbed, or until all the chocolate chips look glossy. Then spread the melty chocolate chips into an even layer - an offset spatula works great for this. Immediately sprinkle with the chopped nuts and sea salt flakes.

Step 6

Chill until firm - I place the pan in the freezer for 30 minutes. Remove pan from freezer, lift toffee out of pan by pulling up on the foil, and transfer to a large cutting board. With a large, heavy, sharp-tipped knife, press into the top of the candy to crack it into pieces. Start toward the outer edge and work your way in. Store in airtight container in a cool place. Keeps very well in the freezer.