Heat oven to 400° F. Generously butter six 6-ounce ramekins (3 1/2-inch diameter); set aside. In 2-cup glass measure, microwave milk and nutmeg on HIGH until hot, about 1 1/2 minutes. In medium saucepan, melt 3 tablespoons butter over medium-low heat. Whisk in flour, salt, dry mustard and red pepper to make a roux; cook 1 minute. Gradually add hot milk, whisking until smooth. Bring to a simmer; cook 3 minutes, whisking frequently. Remove from heat; stir in Kerrygold Dubliner® Cheese until melted. Add egg yolks; mix until blended.
In electric mixer bowl, using whisk attachment, beat egg whites until stiff but not dry. Stir 1/4 of egg whites into cheese sauce to lighten. Gently, but thoroughly, fold in remaining whites until blended. Evenly spoon into buttered ramekins; place ramekins in 13 x 9-inch baking pan. Place pan on center oven rack. Add enough hot water to baking pan to reach halfway up sides of ramekins. Bake until puffed and golden brown, about 18 to 20 minutes.
Meanwhile, in small saucepan, heat balsamic vinegar to a boil over medium-high heat. Boil slowly until reduced to a thin syrup, about 10 to 12 minutes. Remove from heat; set aside.
The soufflés can be served immediately, as is, or cooled and reheated for serving later. To serve immediately, place ramekins on salad plate. Arrange approximately 1 1/2 cups salad greens to the side; drizzle with balsamic syrup.
Twice-Baked Soufflé Variation: To serve soufflés later, cool on wire rack. (Soufflés will fall slightly.) When cool, run small knife along edge to loosen soufflés. Turn out, upside down, onto ovenproof dish. When ready to serve, heat oven to 425° F. Sprinkle about 2 teaspoons shredded Dubliner® Cheese over each soufflé. Season 3/4 cup heavy cream with salt and pepper; pour over tops, covering completely. Heat in oven until tops are light golden, about 10 minutes. Using metal spatula, carefully lift and transfer soufflés to salad plates; serve with salad greens and balsamic syrup as described above.