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.