Outside of your classic cast iron cookware, one of the best investments you can make -- especially if you're a baker -- is in copper. It conducts and holds heat very well; almost too well, in fact, if you aren't accustomed to using copper and suddenly find yourself with a pan full of burned butter and scorched garlic.
A lot of copper cookware, like the skillet that I use for everything from stove-top cooking to broiling, is lined with stainless steel. This makes it easier to clean and less likely to be damaged by certain utensils, but is unhelpful if you want to exploit one of copper's greatest uses: whipping the best egg whites possible.
It's not an old wives' tale: Using a copper bowl really does produce superior egg whites for your meringues and macarons. Trust the French. They've been using copper bowls for centuries. You can even buy antique, hand-hammered French copper bowls that are perfectly usable today, although you'll pay dearly for them.
Why does a copper bowl produce a superior egg white? The copper itself, and the ions that leech into the whites as you whip them. Or, as one PhD puts it:
The copper ions form a yellow complex with one of the proteins in eggs, conalbumin. The conalbumin-copper complex is more stable than the conalbumin alone, so egg whites whipped in a copper bowl are less likely to denature (unfold).
The Mauviel copper bowl seen above costs $120. Not cheap, but properly cared for it will last your entire life (and likely the entire lives of your children and grandchildren). Of course, you can usually scope out the shelves at places like TJ Maxx or Marshall's for discounted Mauviel items, as well as the virtual shelves at outlets like Amazon and Overstock.
But even those won't be cheap cheap, so you should take care of it once you buy it. Like regular copper cookware, you should never put your copper bowl in a dishwasher. Clean it with a little soap and water, then hand dry it. Don't let the copper dry on its own unless you really enjoy vigorously polishing bowls for some reason.
When you do need to polish your bowl, do not ever use copper cleaner on the inside of the bowl -- it will ruin its reactive surface, and the entire reason for purchasing the bowl. You can also use a combination of white vinegar and flour or baking soda and lemon juice to form inexpensive pastes instead of pricey, chemical-laden copper polish. After dishing out for a copper bowl, after all, at least you can save a little on the maintenance fees.