So, I'm on a brownie kick, and am currently playing around with baking batches of brownies in 9"x13" pans. I want each batch to yield 15 brownies (so I'm aiming for brownies that are around 3"x2.5") and I'd like them to look as presentable as possible (e.g. like these guys).   So far, I've read suggestions like:    use a warm blade, wiping it down after every cut let the brownies cool in the pan until room temperature (~ 2 hours), chill in the fridge or freezer, then cut use a plastic knife forgo the entire process and bake in muffin tins.   Do any of the experts here have any time-tested advice? Or if people subscribe to any of the above methods, can they elaborate a bit more? For example, if you believe in the warm blade method, what type of blade would you suggest?  The brownie mix I'm using has chocolate chips in it if that helps anyone. 
a classic European style cheese mongers cutter is perfect. Two wooden dowels with a length of wire between them...actually it is a garrotte for cheese! You have to lift the brownies outof the pan first on foil. Very clean. You can cut when hot and re-cut when cool. Or just use a pastry marker to lay out the grid and then cut to your hearts content. 