Today is National Bittersweet Chocolate Day. So many recipes call for Bittersweet Chocolate or Semi-sweet chocolate in Baking, but what exactly is it? Just an FYI: Bittersweet and semi-sweet are pretty meaningless terms and hard to define.
Generally both bittersweet and semi-sweet have at least 50% cacao. Manufacturers use these terms differently, so the best thing to do is check the cacao percentage. One manufacturer's bittersweet is another's semisweet. I've read (and agree) that 50% and 72% can be used interchangeably when using chocolate for candy making or cut into chunks in lieu of chips. Once you start melting the chocolate and using it in baking, or in mousses and ganaches, the formulas can change. A higher percentage chocolate will bake drier, as it has less sugar, and will require more liquid to emulsify properly for a a mousse or ganache.
Alice Medrich's book Seriously Bittersweet contains formulas for working with different percentages. Older recipes are likely to use something closer to 50 - 55%, and newer recipes are more likely to state a percentage. Something important to know in making the following recipe, if you're substituting sweetened chocolate for the unsweetened chocolate in this Retro Recipe. So watch your ratios.
The Advertisement on the right is a Retro Ad with Recipe from Baker's Chocolate for Bittersweet Chocolate Layer Cake.