⅛tspcoarse Kosher salt(if using table salt, use half the amount)
1 ½tspvanilla bean paste or vanilla extract
¼tspflaky finishing salt(such as Maldon)
Line an 8×8 square baking dish with parchment paper so that the paper hangs over the edges.
In a large, microwaveable bowl (I recommend a glass Pyrex bowl with a 2.5 quart capacity), melt the butter. Whisk in the corn syrup, sugars, sweetened condensed milk and coarse Kosher salt until smooth.
Microwave on high for 6 minutes. Check the temperature by stirring the caramel a bit with the thermometer – it should read between 238-242 degrees to reach the soft caramel stage. If it needs more time, continue to microwave on high in 15-second increments, checking the temperature after each increment.Depending on the power of your microwave, and the temperature of your ingredients when you start cooking the caramel, it may take more or less time. Each time I make this, mine is done at around 6 1/2 - 7 minutes, and I have a 1000-watt microwave. If you have a much higher wattage microwave, start off with less time, so you don't burn your caramel or make it too hard.
Remove the bowl from the microwave - use oven mitts as the bowl will be hot.Stir in the vanilla extract or vanilla bean paste with a spatula. The caramel will bubble and hiss a little.Immediately pour the caramel into the parchment-lined baking dish. Let stand at room temperature for about 15 minutes, then sprinkle the top with flaky Maldon salt or another flaky finishing salt. If you don't have any, just sprinkle with more coarse Kosher salt.
Refrigerate the pan of caramel until firm, about an hour. Lift the slab of caramel out by the paper, and set it on a cutting board.Use a large, sharp chef's knife for cutting the caramel. When you cut it, it should be firm enough to cut cleanly, but not so cold that it's brittle. If it got too firm in the refrigerator, let sit at room temperature for a few minutes before cutting.Cut the slab of caramel into thirds, then cut each third into 15 pieces.
Rip 15 strips of wax paper, measuring about 4 1/2 inches wide each. Then cut the strips into thirds so you have 45 squares of wax paper. Wrap each piece of caramel tightly in the wax paper and twist the ends to secure.
Store the wrapped caramels in an airtight container for up to 2 weeks.
The corn syrup is a necessary component as the combination of the different structure of the sugars in corn syrup and the other sugars prevent crystallization in caramel. Don’t leave it out.
This recipe can be doubled, and I have done it, but be sure your bowl is large enough as this bubbles up quite a bit in the microwave. It will also take longer to reach the correct temperature.
Homemade caramels should be stored, individually wrapped, in an airtight container. They will keep at room temperature for up to 2 weeks - if they last that long! You can also make and wrap them in advance, place in a freezer bag, and freeze for 3-6 months.