1/4 cup ketchup
1/4 cup mayonnaise
2 tablespoons yellow mustard
1 dill pickle, chopped
2 large yellow onions
8 ounces ground beef
1/3 cup shredded sharp Cheddar
Kosher salt and freshly ground black pepper
1 cup milk
1?4 cup vegetable oil, plus more for frying
1 teaspoon baking powder
1 teaspoon onion powder
1 large egg
1 1/2 cups all-purpose flour
1 tablespoon sesame seeds