In a microwave-safe bowl, combine sugar, water, corn syrup, lemon juice, salt.
Microwave on high for 5 minutes, then in 1-minute intervals, stirring after each, until the caramel is just starting to change colour pale golden, 5 to 10 minutes total.
Carefully remove the bowl from the microwave (it will be very hot).
Watch it continue to darken. Meanwhile heat the cream.
After 5 min of darkening, slowly add hot cream. Then stir in butter.
Stir in 1 tablespoon bourbon, 1 teaspoon vanilla extract, 1 teaspoon miso paste, or 1 teaspoon espresso powder, if desired.
Pour the caramel into a heatproof container and let cool completely before using.
