Minnesota Sheet Cake

This is inspired by the famous Texas sheet cake—a large, thin, chocolate cake covered in icing and often pecans. I found that most recipes had a small amount of cocoa in the cake (which just wasn’t enough chocolate for me) and the icing was often too sweet. My Midwestern version of the cake needed a good dose of chocolate, then more chocolate in the form of ganache poured over the warm cake. Black walnuts—candied for plenty of sweet-salty crunch—top the whole thing off, as they are native t