This catch-all category includes a large number of condiments that are slathered or smeared on grilled fare and barbecue before serving. Ketchup and mustard are slather sauces; so are aïoli (Provençale garlic mayonnaise) and romesco (Spanish roasted vegetable and nut sauce). Slather sauces are generally thicker than conventional barbecue sauce. (The exception here is ketchup.) Many contain eggs, oil, or cream, such as tartar sauce, béarnaise sauce, or horseradish sauce.