No one will believe you made these rich, buttery, chocolate-studded muffins at home. Our goal was a moist, just-sweet-enough, generously sized bakery-style muffin with plenty of rich chocolate and butter flavor and a characteristically domed top. Using chopped semisweet chocolate instead of chips gave us a combination of chunks and shards of chocolate pieces. This allowed for the chocolate to meld into the muffin better than chips while also keeping some soft, melty chocolate pockets. Bar chocolate also resulted in zero waxiness at room temperature. Mixing the chocolate in with the dry ingredients instead of folding it in at the end prevented the batter from forming too much gluten, maintaining a tender crumb. To create moist and flavorful muffins, we incorporated sour cream and used nutty browned butter and lots of vanilla. Baking the muffins on a higher rack and at 400 degrees initiated a quick rise to give them nicely domed tops.