American · Cocktail
Two ounces of bourbon, three quarters of an ounce of fresh lemon juice, three quarters of an ounce of simple syrup. Shake hard, pour over ice. That's a whiskey sour, and it's been the template for about half of all cocktails ever since.

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The one thing that matters
Fresh lemon, not the plastic bottle from the back of the fridge. This is a three ingredient drink and there is nowhere for tired citrus to hide.
Spirit, citrus, sugar. Change the spirit and you get a daiquiri or a margarita. The ratio barely moves. Learn this one and you can improvise the rest of the menu.
Maker's Mark is wheated rather than rye-heavy, so it's softer and rounder than most bourbons. That suits a sour, where the lemon is already doing the sharp work and a peppery rye can end up fighting it.
Now the egg white question. Half an ounce of egg white gives you the thick white foam you see in bars, and it changes the texture completely without changing the taste much. If you're doing it, dry shake first with no ice for fifteen seconds, then shake again with ice. Skip it entirely and the drink is still correct.
Two or three dashes of bitters on top of the foam isn't decoration, it's the smell you get on the way in.
Serve it over one big cube in a rocks glass, or up in a coupe if you've used the egg. Goes with fried chicken, barbecue, sharp cheddar, anything salty and heavy.