Butter the top edges of a 2-quart microwave-safe casserole. Add butter, 1 teaspoon of the Diamond Crystal(R) Sea Salt, sugar, and water to the casserole. DO NOT STIR. Microwave on high for 6 to 8 minutes. Check contents for color change. Continue microwaving on high a minute at a time until the mixture just begins to turn a tan color. You need to watch it carefully, and remember: DON'T STIR.
Sprinkle 1/2 cup of the chopped cashews into a 9-into circle on a Silpat mat, parchment paper, or on a buttered baking sheet.
Carefully pour the liquid mixture evenly over the top of the cashews. Immediately sprinkle on the chocolate chips. Allow to sit for 1 minute to melt the chocolate.
Use spatula to smooth out chocolate over the entire sheet of candy.
Sprinkle the remaining cashews and 1/4 teaspoon Diamond Crystal(R) Sea Salt over the top. Refrigerate to cool completely. When cool, break into bite-sized pieces. Store tightly covered in refrigerator.