Add the Irish whiskey to a heavy pot or dutch oven and bring to a simmer over medium heat.
In a bowl, toss the cheese with the cornstarch. Working in 3 batches, gradually stir the cheese mixture into the Irish whiskey until melted. Cook, stirring occasionally, until the mixture is gently bubbling, about 2 minutes; season.
Serve immediately from the dutch oven or transfer to a fondue pot. Serve with brussels sprouts, roasted potato wedges and brown bread chunks.