Meanwhile, heat 1 1/2 cups milk in a large broiler-safe skillet over medium-high heat until just simmering. Whisk the remaining 1/4 cup milk, flour, salt and pepper in a small bowl until combined. Add the flour mixture to the simmering milk; reduce heat to medium-low and cook, whisking constantly, until thickened, 1 to 2 minutes. Remove from heat and whisk in Cheddar, cream cheese and vinegar until the cheese is melted. Stir the pasta and collards into the sauce.