Everything from salads to mac and cheese to sundaes at Stacked is built to customers’ specs. But the Stack Your Own Burger is the best-seller, and although guests can pick from six buns, five patties, nine cheeses, 23 toppings and 13 sauces, the combination that customers choose most is avocado, tomato, cheddar, a fried egg, jalapeno bacon and onion straws on a beef burger with a brioche bun.