Melt butter in a medium saucepan over medium-high heat. Stir in flour until the mixture is smooth.
Stir in garlic and cook until fragrant, approximately 1 minute. Add Guinness, Worcestershire, ketchup, salt, pepper, and sugar. Bring the mixture to a boil, stirring occasionally, until thickened, approximately 6 minutes. Season with additional salt and pepper to taste.
Cover gravy and keep warm on low heat until ready to serve.
In a large bowl, mix together all ingredients for the slaw.
Place fries on serving platter or in skillet. Top fries with corned beef, gravy, and cheese curds.
Pile up slaw in the center and garnish with a sprinkle of freshly chopped parsley.