Prepare the patty by combining the ground beef, garlic powder, salt, and back pepper in a bowl.

Form a round-shaped patty with the ground mixture.

Further, slice the onions into rings, dip them in buttermilk, dredge them with flour, and deep-fry.

Combine mayonnaise, Dijon mustard, Worcestershire sauce, lemon juice, salt, and black pepper in a bowl.

Stir in all the elements to achieve a creamy and smooth texture of the sauce.

Moving forward, grill the patties in a griddle that is grasped with canola oil.

Flip the patties with a tong and let them cook on both sides.

Meanwhile, butter the Texas toast and place it on a pan to toast.

Place a slice of American cheese on top of the patties over medium heat. The heat will help in melting the cheese nicely.

Finally, when everything is done, begin to assemble the burger.

Slather the sauce on the bottom toast and place the cooked patty with melted cheese on top.

Add the crispy onions to the top of the burger and drizzle a teaspoon of sauce on the top.

The copycat Sonic patty melt will be ready.

Serve and enjoy.