Line an 8x8 inch baking dish with parchment paper and lightly grease with butter.

In a microwave-safe bowl, combine melted butter, granulated sugar, brown sugar, corn syrup, sweetened condensed milk, and salt. Stir until smooth.

Microwave on high for 6 minutes, stirring every 2 minutes to prevent burning.

Stir in vanilla extract immediately after microwaving.

Pour the hot caramel mixture into the baking dish and spread evenly. Add desired toppings.

Let cool at room temperature for about 2 hours or in the fridge for 1 hour.

Use the parchment paper to lift the caramels out and cut into squares.