Seven-layer salads are as much about the build and appearance as they are about taste. Just about any ingredient works if you keep the colors varied and the layers clearly defined against the sides of the glass dish. You also need to concentrate the ingredients around the perimeter, where they're visible, and add fewer items as you move inward. Seven-layer salads typically start with lettuce on the bottom, but you can change the order of ingredients as you see fit. You also need a trifle bowl -- the clear glass bowl with straight sides -- to display your creation.
Roughly chop enough iceberg lettuce, romaine and mixed greens to fill about half the bowl. Add a 2- to 3-inch layer of chopped lettuce to the bowl and spread it out evenly.
Arrange a 1-inch layer of roughly chopped or sliced vegetables on the lettuce and against the sides of the dish. Check how the layer looks from the side and straighten it up as needed. Add another layer of vegetables on top of the first. Tomatoes, mushrooms, cucumber, bell peppers, celery; any salad vegetable works. Fill in the center with a little chopped lettuce.
Arrange a 1/2- to 3/4-inch layer sliced, chopped or shredded ingredients in the bowl. This is where you want to add proteins, such as hard-boiled eggs, chicken, bacon or ham, and finishing ingredients, such as peas, shredded cheese and sliced scallions. Fill in the center with chopped lettuce as needed.
Straighten the ingredient layer as needed for neatness. Add 2 more 1/2- to 3/4-inch layers of sliced, shredded or chopped ingredients on top of the first; straighten these layers for neatness as before. Serve the salad as-is or add dressing.
Spread a mayonnaise-based dressing around the perimeter of the bowl and evenly on top of the salad from edge to edge, if desired. Mayonnaise and yogurt, buttermilk ranch, Thousand Island, creamy Italian -- anything mayo- or cream-based works.
Garnish the salad with a few of the remaining chopped ingredients. Chill the salad in the refrigerator until you're ready to serve.
You don't need seven layers of ingredients for a seven-layer salad, but you need at least four or five to make the intended visual statement.