* If you're talking about a quantity of potatoes: "Des pommes de terre" (pronounced "deh pom duh tehr") is the most natural way.
* If you're talking about a specific amount, you'll need to specify:
* "Un peu de pommes de terre" (pronounced "un peu duh pom duh tehr") - a little bit of potatoes
* "Quelques pommes de terre" (pronounced "kelk pom duh tehr") - a few potatoes
* "Deux pommes de terre" (pronounced "duh pom duh tehr") - two potatoes
Remember that French uses the definite article "des" before plural nouns when referring to a general quantity.