Courtesy of Alton Brown
2 tablespoons unsalted butter
2 tablespoons all-purpose flour
1 teaspoon Dijon mustard
1 teaspoon Worcestershire sauce
1/2 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1/2 cup dark beer, such as stout or porter
3/4 cup heavy cream
6 ounces (1 1/2 cups) shredded cheddar cheese
2 drops hot sauce (optional)
Melt the butter over medium-low heat in a small saucepan. Whisk in the flour and cook, whisking constantly, for 2 to 3 minutes, being careful not to brown the flour.
Whisk in mustard, Worcestershire sauce, salt, and pepper until smooth. Add the beer and whisk to combine. Pour in the cream and whisk until well combined and smooth. Gradually add the cheese, stirring constantly, until the cheese melts and sauce is smooth, 4 to 5 minutes. Add the hot sauce. Serve immediately.
When reheating, use an immersion blender to bring it back to the right consistency.