Line a cookie sheet, large casserole dish, or similar flat surface with parchment paper or a silicone baking mat and set aside.
Grease (I use a little extra butter) a 2-qt (or more) high heat microwave safe bowl, then add the brown sugar, butter, water, and vanilla (do not stir).
Microwave on high for 6 minutes, or until mixture bubbles in the center for around 3 minutes and starts to get a deeper shade of brown (it will also get a 'nutty' scent when you open the door). If you have a thermometer, you want it between 300°F - 310°F. Add additional time in small increments to prevent burning it (it generally takes me around 6-7 minutes total in a 1000W microwave, depending how many times I pause and check it).
Using oven mitts (it will be extremely hot), remove the bowl and pour the molten sugar onto the parchment paper lined tray (the butter may separate a bit; this is normal since we’re fast-cooking this). Immediately add the chocolate chips over top of the hot sugar.
As they begin to melt, use a spoon or spatula to spread them out evenly, then top with the sea salt (or chopped nuts or other decorative items if desired).
Cool in the refrigerator until firm (about 30-40 minutes).
Break into pieces (use your hands or a rubber mallet) and store in an airtight container in a cool, dark place.
