Stir flour and 2 tablespoons milk in a small bowl to make a smooth paste. Heat the remaining milk in a small heavy saucepan over medium heat until steaming. Whisk the flour paste into the hot milk and cook, whisking constantly, until thickened, about 1 minute. Remove from the heat and whisk in cottage cheese, Swiss cheese, salt and white pepper. Transfer the sauce to a food processor or blender and puree until smooth. Serve over steamed vegetables and top with Parmesan and breadcrumbs, if desired.