To simplify this drink and break it down, it is essentially is a pour of whiskey over ice, that is both sweetened and seasoned. As simple as that sounds... it's a classic that still stands out since its' creation almost 200 years ago.
The cocktail was first conceived by adding a spirit, sugar, water, and spices/bitters. An Old Fashioned Cocktail hits all those marks. I recommend starting with top ingredients, such as your favourite whiskey, my key takeaway here is; 'If you wouldn't sip it neat, don't put it in your cocktail'. If you fancy making it a non-alcoholic Old Fashioned cocktail, try Lyre's American Malt non-alcoholic. You also have the option of using a sugar syrup or muddling sugar and bitters.
Sugar syrup will save you time if you are in a hurry, however, if you want to make the drink the old fashioned way (see what I did there...) as they did back in the 19th century, granulated sugar or a sugar cube is the way to go. If you want to make the cocktail with more of a modern twist, opt for simple syrup, such as Monin syrup. Just know that simple syrup adds a bit more water to your drink, so you may need to adjust your ice and stirring accordingly.
Once you’ve mastered the Old Fashioned, I highly recommend you also try making the cocktail with rye whiskey instead, which results in a slightly spicier drink. If you or a guest is not a whiskey fan... you can replace it with rum, brandy, or any number of spirits. But there’s something about the bourbon-spiked version that drinkers have been coming back to for decades, so why mess with perfection?