Line your prepared baking sheet with a silicone baking mat or parchment paper, and set it aside.
In a large glass, microwave-safe bowl (4 quarts is best), combine the butter, sugars, salt, water, and corn syrup.
Microwave for 3 minutes on HIGH.
Stir in the chopped nuts.
Microwave for 8-10 minutes on HIGH or until it reaches 300°F (149°C) on an instant-read or candy thermometer. Pause the microwave cooking every 2 minutes to stir and check the temperature. Do NOT overcook it, or it will burn.
Quickly pour and spread the mixture onto a silicone-lined baking sheet in an even layer, about 1/8 inch thick.
Add the chocolate chips on top and let them rest for 3 minutes to melt. Using an offset spatula, gently spread the melted chocolate over the top. Sprinkle on the nuts and sea salt.
Chill until set, about an hour. Break into pieces.
Notes
-My microwave is 1,000 watts. If yours is lower, you may need to cook it slightly longer (1-2 minutes). If yours is higher, you may need to cook it a minute less.-I would not recommend doubling the batch but instead making two separate batches.Adapted from Genius KitchenSTORE the toffee in an airtight container at room temperature, where it will stay good for up to two weeks. To FREEZE, place the toffee in a freezer-safe bag or container, separating layers with parchment paper. It will last up to 3 months frozen.To REHEAT, let it thaw at room temperature and avoid microwaving, as it can cause the chocolate to separate and change the toffee’s texture.