Their site says that they’re not really regular brownies, they are a hybrid of brownie dough and chocolate chip cookie dough, marbled (and probably with some variations from traditional recipes to make that combination work). If you ever order them, you can figure out how big the pan is, because they claim they give (sell) you the whole pan of brownies sliced into 9 pieces. I’ve never had them, but from the photo I’m going to guess the pan is maybe 6 or 7 inches on a side, and specially made for their recipe and ovens.
Their site says they are about 7 1/2 inches square.
Round pan? Put in pie crust, add melted marshmallows for fluffier batter, and you have hot fudge pie