Green beans, string beans, snap beans, haricots verts—whatever you like to call ’em-are the simple, stringy veggies that have graced practically every dinner table. Especially around the holidays.

Cooking a green bean casserole may seem straightforward, but common pitfalls do exist. Here are some expert tips to keep in mind when making one.

“Americans just do not know how to cook green beans,” said Ann, a Bayfield Farmers Market vendor, as she handed me a sack of deep green, plump beans she picked earlier that morning. “When they’re ...