Super article from Jason Wilson. Below is some great advice on using a classic recipe and doing some simple tweaks to come up with something different and original.
In fact, without trying to ruin the livelihoods of mixologists with well-paying corporate gigs, here’s their basic, not-so-secret formula for almost all new cocktail development: Take a classic recipe from the 20th century. Replace the base spirit with another base spirit (either whatever you have on hand or, in the case of corporate mixologists, the product of whoever is paying you). More advanced home bartenders can alter the secondary spirits, change the juices, add different bitters or bring in new mixers.
For instance, switch out bourbon for apple brandy, and simple syrup for maple syrup, and your Old-Fashioned becomes an Apple Brandy Old-Fashioned. Replace gin with aquavit, and lemon with lime, and your French 75 becomes a Swedish 60. For your Manhattan, use bianco vermouth instead of sweet vermouth, replace bitters with a strange root-tea liqueur called Root, and you have a Pennsylvania Dutch Manhattan.
The article goes on to talk about some great cognac cocktails. I definitely agree with him - a cognac based Sazerac is wonderful (Old-Fashioneds too!)