Whisk 2 Tbsp. milk and flour in a small bowl. Heat the remaining milk in a small saucepan over medium heat until little bubbles form on the surface, about 3 minutes. Whisk the flour mixture into the hot milk; cook, stirring constantly, until slightly thickened, 1 to 2 minutes. Whisk in cheese, salt, cumin, nutmeg, and cayenne; cook, stirring constantly, until the cheese is melted and the sauce is thickened, 1 to 2 minutes. Stir the cheese sauce into the kale mixture.