Caramel Sauce

Stir the sugar, corn syrup, water and lemon juice together in a 2-cup microwave-safe measuring cup or medium glass bowl. Microwave until the caramel is pale yellow, or just barely starting to take on some color, 4-8 minutes (depending on the strength of your microwave). It's fine to stop and open the microwave to check often; just don't let it get too dark or it will burn. Let the caramel sit until it turns a rich amber color, about 5 minutes. (If after five minutes, it's not dark enough, place it back in the microwave for thirty seconds or so, then let it darken again.)

In the meantime, heat the cream in the microwave until hot. Once the caramel reaches the right color, immediately stir in the hot cream a few tablespoons at a time. It will bubble up intensely, but it won't overflow. After you've added all the cream, stir to incorporate, then add the butter and salt. Add more cream if the mixture seems too thick. Once the caramel cools, you can store it in your fridge.