There are lots of recipes out there for Irish Coffee, and some of them include things like whipped cream from a spray can, maraschino cherries, and even creme de menthe.
These additions can be fun to jazz up the usual cup of Irish Coffee - try drizzling green creme de menthe over the cream in the shape of a shamrock for St. Patrick's Day, for example. But for purists, this is the recipe you're looking for.
If you can, serve Irish Coffee in clear glass mugs that have been gently warmed in hot water first. The finished coffee will have three distinct layers: the coffee on the bottom, the cream on the top, and a middle layer where the coffee and cream have slightly mixed.
You can rim the mugs with white granulated sugar (or green decorator's sugar) for a festive look, but this really isn't necessary. The taste of the drink itself really needs no extra sweetness.
Serve the coffee as soon as it's been made, and sip it through the cream layer on the top. Don't stir! Make sure you also serve your guests some napkins to remove the cream "mustaches" that will appear on their upper lips!
For each serving, you will need:
Pour whiskey into the bottom of a warmed coffee mug. Add brown sugar and hot coffee; stir to combine.
Gently spoon several tablespoons of cream over the top of the hot coffee mixture. Do not stir! Serve immediately.