Line a 7x11 baking dish with foil and heavily spray with butter-flavored cooking spray. Set aside. In VERY large mixing bowl, melt butter in microwave. My bowl is a heavy-duty Pyrex 4.0 Liter bowl. DO NOT use a smaller bowl! If you don't have a big enough bowl, just make a half of a recipe in a large bowl. Reason being, this bubbles up and you DO NOT want it to boil over!! After butter is melted, stir in rest of ingredients well. Microwave on high for 11-12 minutes stirring after every 2 minutes. Stir when done, stir in vanilla and pour, carefully, into prepared baking dish. Let sit 5 minutes and sprinkle with salt if desired. *Salt brings out the flavor and makes it even more delicious. Put into fridge and let cool for 20-30 minutes. Cut with long, sharp knife oiled constantly with butter for easier cutting. Wrap pieces in waxed paper or parchment paper. Store at room temp in airtight container.