Anyone who’s tried making Rome’s signature pastascarbonara, Amatriciana and gricia, all derivatives of trendier-than-thou cacio e pepe—knows that simple ingredients do not a reliable recipe make. In fact, it’s just the opposite. There’s no room for misfires when a recipe counts water as one of its few ingredients.

When Milk Street editorial director J.M. Hirsch traveled to Rome to trace the family tree of these famous pastas, he learned this first hand: Neither cacio e pepe nor carbonara were as straightforward back at home as they seemed in the glow of the Eternal City.

For one, the pecorino Romano in Italy is saltier than it is stateside. And salty cheese mixed with starchy pasta water is less prone to clumping when it melts—hence Italy’s effortlessly smooth cacio e pepe.

If you thought the solution would be to use imported cheese, you aren’t alone. Unfortunately, though, this didn’t help much, thanks to another hurdle. By the time imported cheese turns up in American markets, it’s no longer fresh, and older cheese clumps more readily than fresh cheese, it turns out. The Italians had two legs up that our kitchen needed to contend with.

What we needed was more starch. So, we added starch to the equation.

Cornstarch, that is.

It’s a secret weapon that the Milk Street test kitchen uses frequently, and in the case of cacio e pepe—and carbonara for that matter—it proved just the ticket for a clump-free consistency.

When making cacio e pepe, simply stir the cornstarch into the water you’re using for the sauce, before adding in the grated cheese. (Use the small holes of a box grater for the best melt.)

A little cornstarch goes a long way. Just two teaspoons is enough to produce a smooth sauce that’s so stable, it even reheats well. Talk about staying power.