Best way to cleanly cut brownies?

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.

I can't select either of the above answers as the best answer for the following reason:

The brownie I'm making is meant to be "gooey", and even after cooling for 2 hours, and then chilling in the fridge for another 30 minutes, the the upper-half brownie still remained fudge-like. I ended up using Jay's suggestion to eye-ball a 4x4 grid, however I didn't use a hot knife. I used a plastic knife with an up-and-down sawing motion and got fantastic results. The cuts were as clean as you could ask for, and the entire process didn't take more than 5-10 minutes.

As an aside: I decided to forgo the "aluminum foil sling" and just spray the 9"x13" pan with PAM, line the bottom with parchment paper, and spray it down one more time. The brownie "loaf" came out with zero fuss and had a perfect looking crust.

edit: I plan on experimenting with 2 large metal rulers to score the loaf, instead of eyeballing the grid.

I have had pretty good success with the warm blade method. For this, I would suggest letting them cool to a little warmer than room temp. Then, using a warm, very thin knife (you can warm it by dipping in a pan of hot water, then wiping dry), cut the brownies. However, DO NOT remove them from the pan yet. Once they are cut, chill them. Then, use a knife to "recut" along your earlier lines. This will take care of any bits that sort of remelted together from chocolate chips and so on. Now, use a thin metal spatula to carefully remove. All that said, I am a big fan of the muffin cup method. Make sure to liberally use a pan spray or butter the compartments so they come out nicely. I usually wouldn't go to all this trouble since people eat brownies too quickly to care what they look like, but if you are doing them to sell or for a fancy event, either of these would work.

Have you tried using (unscented) dental floss? That would fix the main issue, that the brownie sticks to the knifes surface on the way down.

The main reason why brownies become mal-formed when you cut into them is because the pressure of the knife cutting in the downward motion AND the sticky brownie sticking to the knife and being "dragged" downward as it is being cut.

Generally to get a even nicely shaped brownie cube, the brownie should be baked well enough so that it is not gooey anymore. A lot of recipes are for "really soft gooey at the center" brownies that can become easily malformed. Make sure to bake a brownie sufficiently so that it is done well enough to hold its shape.

You should definitely let the brownie first cool. The cooling process allow the brownie to continue cooking and set. Most brownie recipe also factor in this cooling step into bake time. At that point, you should use a very sharp thin knife(to reduce the amount of pressure). In the past, I have tried the warmed blade method by placing the knife under hot tap warm. I then dry it and lightly oil it with canola oil before cutting into the brownies.

Another thing I've tried in the past is to let the brownies cool in the pan but when it was time to cut the brownie after cooling, I pop the brownie out of the pan first. This makes it easier to cleanly cut AND you will also avoid scratching your brownie pan. But becareful. This cannot be done for all recipes of brownies.

Lastly, as in my comment to your question, it would be easier to evenly cut the brownies into 16 brownies per batch. You would cut it 4 x 4 to yield 2.25 x 3.25 brownies. It is easier to cut 4 x 4 because you can cut down the center of the brownie and then cut down the center of each sides. It is easier to eye ball where the half line is rather than eyeballing how to evenly cut into 5 equal parts if you are doing 3 x 5.

EDIT: According to your comments you decided you might go with the muffin tin method. If you do that, I would suggest instead to go with the muffin's relative, cupcake method. Just use cupcake liners to avoid having to deal with a large amount of nonstick spray.

definitely let them cool, remove them from the baking dish (hopefully you used parchment paper and this step is problem free), then flip them, then cut them as usual. the shiny shell-like top doesn't fracture and get mutilated as much when cut this way.

I let my fudgey brownies cool & then I use a lightly oiled, serrated bread knife with a gentle sawing motion & a gentle downward pressure. I clean then re-oil the knife between cuts. Serrated knives are much better for any cakes or pastries that you do not wish to crush.

I use a very sharp small spatula using the up and down motion after I put in freezer for a half hour or more. Works pretty well (but I am still looking for an even better solution).

Pizza cutter along with other suggestions

cookie cutters. :) But I have used the plastic knife method with good results. Just make sure they are not too hot, it will melt the plastic.

Try a pizza cutter instead of a knife.

In my kitchen I have two cutters that have three (3) blades each. They blades are adjustable so that they can be spaced to the desired width. With two cutters there are many combinations that can be set and left that way for the next time.