Melt butter in a large skillet over medium heat; add onion, and sauté until tender. Stir in diced pimiento and roasted green chiles, and sauté 1 minute. Set aside.
Process 1 cup cottage cheese in blender until creamy.
Place onion mixture, cottage cheese, and cubed cheese in a 4-qt. slow cooker; stir in evaporated milk. Cover and cook on LOW 1 hour and 20 minutes, stirring gently every 20 minutes. Stir before serving. Serve with assorted tortilla and corn chips and desired toppings.