How Do I Make Pesto Sauce Stick To Pasta?

Extruded pasta using a bronze die

Short answer
The most effective way to make a sauce stick to pasta is to buy pasta that has been made using a "bronze die." It will be a bit more expensive than you might be used to, but this kind of pasta has a rough surface, which means sauces can't help but stick to it.

Long answer
When trying to make pesto (or any sauce for that matter) stick to pasta, the biggest gains are to be had from buying the right kind of pasta.

The dried stuff you find in the supermarket is made from a simple semolina and water dough that has been extruded through a die and shaped. Budget pasta will have been extruded through an aluminium or Teflon die, resulting in a smooth surface texture. There's nothing wrong with that per se, but the premium pasta in your local deli will almost always have been extruded through a bronze die. This results in a rough texture that dramatically increases the surface area of the pasta, thereby ensuring maximum stickiness.

The shape of your pasta is crucial too. While thick, ragù-style sauces are bold enough to stand up to big shapes like pappardelle and rigatoni, with pesto, you want shapes like fusilli or trofie, which have plentiful bends, grooves, twists, and troughs. These provide your pesto with the maximum number of places to hide.

As for the sauce itself, well, pesto is naturally pretty good at clinging to pasta. The secret to making it even stickier is to mix it with a little bit of the water you cooked your pasta in. This water is bursting with starch and acts as an emulsifier and a thickener, giving you the best possible chance of serving a restaurant-quality dish.