You'll need:
1 tsp sugar
1 thick orange slice
2-4 dashes bitters (like Angostura)
2-3 oz Rye whiskey (though I also love this drink with bourbon)
ice
Slice your orange thickly, then cut the slice into quarters. Layer your orange, sugar and bitters in your "old fashioned" glass. With a muddler (or the end of a wooden spoon), muddle the orange, mixing until the sugar has dissolved. Now add the ice and the whiskey and stir the cocktail, making sure all the flavors are mixed. Traditionally, this is served with a maraschino cherry, but I like it less sweet, so I normally don't use them. Enjoy!