Heat milk in a microwave-safe measuring cup in the microwave until hot, about 1 1/2 minutes. Melt the remaining 2 tablespoons butter in a small saucepan over medium heat. Add flour and cook, whisking constantly, until a nutty aroma develops, about 2 minutes. Slowly whisk in the hot milk. Bring to a simmer and cook, stirring, until bubbling and thickened, about 2 minutes. Remove from heat. Whisk in nutmeg, salt and pepper.