In a microwave safe bowl, melt the butter completely.
1/2 cup (111g) salted butter
Add the brown sugar, corn syrup and sweetened condensed milk to the bowl and whisk until completely combined.
2 cups (492g) brown sugar, 1 14 oz can sweetened condensed milk, 1 cup (327g) corn syrup
Microwave on high power for 5 minutes.
Stir and check the temperature of the mixture. Our goal is to get it to about 240°.
If you don't have a instant read thermometer, you can check the doneness by dropping a small spoonful into a cup with ice water. The texture of the caramel after it cools down in the ice water is what the texture of the caramel will be if you stopped cooking it right now. It should be soft and pliable, but not super hard or super soft.
If needed, return the caramel to the microwave and cook for an additional one minute and then check the temperature, repeating until the temperature has reached 240°f (115°c) or until it is done to your liking by the ice water test.
Stir in the vanilla extract.
1 tsp vanilla extract
Pour the caramel mixture into a buttered 8x8 pan.
Allow the caramel to cool at room temperature for 30 minutes.
Then place the caramel in the fridge for 2-3 hours or until set.
Sprinkle with flakey sea salt, if desired.
flakey sea salt
Cut into desired shape and size, wrap in wax paper. Enjoy!