01 -  Cook pasta shells or elbow macaroni in a pot of salted boiling water until al dente. Drain thoroughly and set aside. 
 02 -  In a large skillet, warm oil over medium heat. Sauté diced onion until translucent, then add ground beef. Cook thoroughly, breaking up meat with a wooden spoon, until browned. Season with salt and black pepper. 
 03 -  Lower heat to medium-low. Stir in ketchup, yellow mustard, whole milk, cream cheese, and half of the shredded cheddar cheese. Mix until cheese melts and sauce becomes smooth. 
 04 -  Gently fold cooked pasta into the beef and sauce mixture. Toss to coat evenly. Sprinkle remaining cheddar cheese over the top, cover the skillet, and let cheese melt for 1 to 2 minutes. 
 05 -  Top with chopped dill pickles. Garnish with additional cheddar cheese and sesame seeds if desired. Serve immediately.