How to Make It
In a blender or food processor, puree the parsley, the smashed garlic, the capers, and the anchovy paste with the olive oil, the wine vinegar, and the salt and pepper.
In a large pot of boiling, salted water, cook the penne rigate until just done, about 13 minutes. Drain.
In a large bowl, toss the pasta with the parsley mixture, mozzarella, and tomatoes.
Fresh Mozzarella: Fresh mozzarella is a soft, white cheese formed into a ball, which is usually packaged with water in plastic tubs to keep it moist. The cheese has a mild, milky taste that combines well with other, stronger flavors, and melts to a nice oozy texture. It's becoming more and more available in grocery stores; we have seen the Poly-O brand in many locations. Drain the cheese before using. Test-Kitchen Tip: Cut the mozzarella into cubes first thing and let it sit at room temperature while you prepare the rest of the recipe. That way the mozzarella will melt more quickly.