Line an 8 x 8-inch baking dish with parchment or butter the pan.
Melt butter in a large microwave-safe bowl. Stir in corn syrup, sugars, sweetened condense milk until combined.
½ cup salted butter, ½ cup light corn syrup, ½ cup brown sugar, ½ cup sweetened condensed milk, ½ cup granulated sugar
Microwave for 6 minutes. All microwave ovens differ slightly in timing. In my microwave, 6 minutes and 30 seconds is the perfect time. To test caramel doneness, add ice cubes to a glass of cold water. Drop a small spoonful of caramel into the water. If it's too soft, cook another 30 seconds.
Carefully remove the bowl and quickly stir in the vanilla. Being mindful that the mixture is hot, pour it into the prepared baking dish. Let it cool for a few minutes, and then top with flaky sea salt if desired. Chilling in the refrigerator until cold speeds up the process and makes cutting easier.
1 ½ teaspoon vanilla
Once set and cold, cut the caramels using a pizza cutter. If the caramels are room temperature, spray the cutter with nonstick cooking spray. Store in candy wrappers at room temperature or freezer for longer storage.
Notes
Butter: Use salted butter for the best flavor balance.
Microwave Bowl: Choose a large microwave-safe bowl—the mixture bubbles up while cooking.
Microwave Power: Times may vary slightly depending on microwave wattage; aim for about 6 minutes.
Flavor Boost: Stir in vanilla at the end for classic caramel flavor.
Storage: Wrap each piece in wax paper to keep them from sticking together.