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It's impossible to have a well-stocked bar without orange liqueur. Except we don't actually ever call it orange liqueur. We call it curaçao or triple sec. Online cocktail forums are full of some serious Kirk-vs-Picard level of nerd arguments about the differences between the two liqueurs. If you don't really want to get into it, though, it's safe to assume that a curaçao is generally dark with a brandy base (like Grand Marnier) and triple sec is clear with a neutral spirit base (like Cointreau).
What's Available to Buy
Orange liqueur, in one form or another, is easy to find at any liquor store. Grand Marnier is the only curaçao that I've liked so far, though Pierre Ferrand recently released an intriguing version worth checking out. In the triple sec category, Combier and Patron Citronge are both good but are second choices next to Cointreau. The less-pricey brands tend to taste overly sweet with a harsh bite. They taste, in a word, cheap.
When mixing drinks, I've found that Grand Marnier tends to go best in cocktails with aged spirits and Cointreau seems best in drinks made with clear spirits. Neither of them is out-of-this-world expensive, but keeping both on hand costs about $60. I've found that I'm a little wary of "wasting" either in untested recipes. I tried keeping the cheap stuff on hand as a back-up, but that just resulted in gross drinks. In the orange liqueur world, there was a top shelf and a bottom shelf. I wanted a middle-shelf liqueur, so I had to make it myself.
DIY orange liqueur saves a little cash, but more importantly, its flavor profile is a good match for a wide variety of spirits and cocktail ingredients. The mix of navel and bitter orange peels along with brandy and vodka gives it a flexible, sweet-but-not-too-sweet flavor that makes for well-balanced cocktails. It isn't as refined as Grand Marnier or Cointreau, but it comes close enough that I'm happy to use it in my Sidecar or Cosmopolitan as well as in more experimental concoctions.
A side-by-side comparison of homemade orange liqueur with a bottom-shelf triple sec is no contest—DIY wins it by a mile. If you're feeling adventurous, mix up a special batch with some extra spices or flavorings. I made a batch with cinnamon and cloves that pairs well with rum and whiskey, and I think vanilla could make for a fun addition, too.
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It would be quicker to list cocktails that don't contain orange liqueur than to list the ones that do. This stuff really is essential, and you'll see it in a wide variety of drinks from sours like the Margarita and the Derby to fruity fare like Lusty Red Sangria and Cider Sangria.
Orange liqueur pairs well with Cognac or rye, like in the Morning Glory. You can even keep warm with Orange Pisco Hot Chocolate and Mulled Apple Cider. It's also a great addition to crepes, chocolate mousse, cheesecake, and biscotti. You may find yourself making orange liqueur by the gallon once you see how useful it is.
About the Author: Marcia Simmons is the co-author of DIY Cocktails: A Simple Guide to Creating Your Own Signature Drinks. She also shares cocktail recipes and tips on the DIY Cocktails blog and on Twitter @DIYCocktails.