Anchovies can be substituted with some extra capers and olives, for added saltiness. Miso paste is a great vegan and vegetarian alternative, as it can add that umami and savory taste the sauce needs; if possible, opt for darker varieties, like brown or red miso, and add a little at a time. Sundried tomatoes can be added thinly sliced to the sauce for their rich umami and tangy flavor, and offer a great vegan pasta alternative. All substitutes won't offer the same taste as anchovies or anchovy paste, but will prepare a great recipe.