I solve this task on a somewhat regular basis with the blank containing "alcoholic" - so to challenge myself for the task, I decided I had to go with the opposite. To my mind, the quintessential non-alcoholic beverage is cola, so I figured I'd design and produce a cola drink.

One problem: cola recipes that try to exactly duplicate Coke or clone alleged versions of its secret formula are full of things like essential oils that you probably don't have. OpenCola, which is the gold standard, involves eight different essential oils, plus gum arabic. To my mind all these recipes have a huge problem - you can't decide on the spur of the moment to whip up a nice glass of OpenCola. Instructables has a version that seems promising, but doesn't really capture what I regard as the essential cola flavor. It's close, but something is missing.

Looking over the ingredients list for OpenCola, I realized what it was. OpenCola is reported to taste almost exactly like Coke; its flavors are citrus (orange, lime, lemon), spice (cassia, nutmeg, coriander), and floral (lavender and neroli) in nature. The floral taste is hard to notice, at least to me, but Fakola (the instructables clone) doesn't handle either the citrus or the spices very well. With reference to that and another version that seems particularly off the mark, I cobbled together my own version of a cola recipe. It is not my intent for this to duplicate Coca-Cola perfectly, but I do intend to make something that captures the essence of cola flavor. I also started off trying for something you could prepare in a couple minutes whenever you felt like a glass of coke, but decided at the end to go with a syrup which can be made ahead and kept in the fridge. It's still much less of a pain to prepare the syrup than it is to follow the OpenCola recipe.

All of the versions of the recipe which follow are based on the assumption of a 12-oz glass made by adding seltzer to the specified ingredients.

Recipe (first pass):
1/4 t mixed fresh-ground anise, coriander, and nutmeg (use more if previously ground)
1/4 t cinnamon, fresh-ground (use more if previously ground)
1 1/2 t key lime juice
2 Tb sugar

Comments:
A little bit too spicy, and definitely way too much coriander (unsurprising, since it's proportionally more than in OpenCola). It also has the wrong mouthfeel. I tried a can of Coke for comparison, and found that it had more of a side-of-the-mouth feeling to it, so I added half a teaspoon of black coffee. Amazingly, this helped a lot - but it's still not right. Too thin, for one thing.

Recipe (second pass):
Spice mix: 4 parts fresh-ground cinnamon, 2 parts fresh-ground nutmeg, 1 part fresh-ground anise
1/4 t spice mix
1/4 c sugar
1 t key lime juice

Comments:
There's a slight bitterness missing; coffee resolves this, but it takes a full teaspoon, which leaves too much of a coffee smell for anything other than trying to clone Coca-Cola Blak. Since I don't like coffee with my cola, this is annoying. And of course there's the faint graininess of the ground spices. At this point I'm ready to say that if you like whiskey or chocolate in your cola, this is a good version for that; if you like it straight or with vanilla, you'll notice what's not quite right about it.

Recipe (final):
1/4 t spice mix above
1/4 c sugar
1/4 c water
1 t key lime juice

Comments:
This version is largely the same as above, but with some technique added. You bring the sugar and half the water to a boil, and cook until it starts to turn yellow. Then, add the other ingredients, and remove from the heat. Stir vigorously to dissolve as much of the candy-like caramel syrup in the water as you can; it will probably require applying gentle heat to get it all in.

The resulting syrup should actually be made in larger quantities - I started with a double batch, which I regard as minimal. You need 1/4 c of the syrup per 12 oz glass. It doesn't taste like Coke - I knew it wouldn't from the moment I started - but it is a refreshing and delicious cola beverage. For my money, the anise actually adds something that now feels like it's missing from the commercial version. On the other hand, there'll be spices settling at the bottom of the glass, and drinking little grains of spice isn't fun. I'm tempted to start decanting it in the future.

By the way, it's worth considering some of the classic coke variations. One from the old-time soda fountains is to add a teaspoon or two of chocolate syrup - traditionally a relatively thin brand such as Fox's U-Bet, though I taste-tested this variant with Hershey's since that's what we have in the fridge. It's very good. Alternatively, consider a splash of vanilla extract, maraschino cherry juice, or grenadine, or a shot of bourbon or rum.