This "Make Your Own Old Fashioned Bar" Idea Is Genius

Now, let's talk about why "built" cocktails like the Old Fashioned -- i.e. cocktails you can make right in the cup, not in a shaker or mixing glass -- are ideal for parties. First, they're just practical. When you eliminate tools, you eliminate mess. Second, these are the least diluted, warmest cocktails. That means you won't be cycling through tons and tons of ice, and there's generally less added water to control (finicky dilution is often the culprit in a badly mixed drink).

These cocktails are also traditionally "sipping" drinks, which taste heavily of their base spirit, and are meant to be enjoyed slowly. The essence of any built drink is slow change over time. The first sip should taste fairly boozy (remember, you're meant to sip them, not pound them), but then the cocktail should stay balanced over a wide range of dilutions (since the ice in the glass will melt over time, ideally making the drink more refreshing as it goes). This ability to stand up to both a little and a lot of dilution is what makes these drinks the most forgiving for inexperienced guests to make themselves -- you really can't mess them up.

Finally, Old Fashioneds and other built drinks don't need acids like lemon or lime juice, which means less mess and prep work. Acids don't maintain balance over a range of dilutions (which is also why you shouldn't serve a sour on the rocks). If the drink needs brightness, use essential oils instead. Lemon, orange, and grapefruit twists work well, which is why you typically see an Old Fashioned served with citrus peel.

In summary, this category of drinks is (1) the least messy to mix, (2) requires the least amount of tools and ingredients, and (3) is very forgiving -- a little too much or too little dilution won't throw the drink out of balance, making them very hard to mess up.

The hardest part of serving a built drink at a party is that they generally call for one large ice cube, because you want the ice to melt slowly over time, and it's not exactly smooth to make your guests go find your freezer whenever they want a fresh drink. You also don't want to use an ice bucket, which will get all melty at the bottom and defeat the purpose of the large cube by adding excess melt water to the drink. 

My solve for this is a cooler rack, like this one from Igloo. Have a designated ice cooler near your Old Fashioned station, and fill the bottom portion with ice packs, dry ice, regular ice -- whatever floats your boat. Then add a rack that hovers above this layer of regular ice, and store all of your perfect large cubes on that rack. Any excess melt water will drip down through the rack and not accumulate on the ice itself, and a cooler keeps ice much colder than an ice bucket does. 

When I assemble the bar itself, I like to include three spirits and three syrups, along with some fun bitters if I have them (if not, regular Angostura work just fine), and then let the guests mix and match flavors. For this to work, you want all your spirits in the oaky or smokey category -- think bourbon, rye, mezcal, rum, or even (one of my favorites) an oak aged gin. For this bar, I used a pecan-infused bourbon, a rye, and mezcal. 

For syrups, I make things easy on myself by using real maple syrup as one option, then including two that are more out of the box. Here I went for a honey lavender syrup (which also kills it in lattes), and a concord grape syrup, since they happened to be in season at my local farm market. Your guests can then decide which syrup they want to pair with each spirit every time they fill their glass. Just make sure they know the general proportions of the drink (two ounces spirit, two dashes bitters, half ounce syrup), or -- better yet -- have a tablespoon out to measure the syrup (1 tbsp = 1 half ounce, i.e. the correct serving for each drink) and a 2 oz jigger or shot glass out to measure the booze. 

You can include themed garnishes as well (like the bee pollen, lavender, pecans, and concord grapes I used here), or a variety of citrus peels. Large ice cubes make great trays for any aromatic garnish you want to balance right on top.