Trim the green beans, removing the tough stem ends. Bring a large pot of water to a boil and add the kosher salt.
Add them to the boiling water and cook until crisp-tender and bright green, 3–5 minutes. Drain and rinse under cold water to stop cooking, then pat dry.
Heat the olive oil and unsalted butter in a large skillet over medium-high heat until the butter foams. Add the garlic and cook, stirring, until fragrant but not browned, 30–60 seconds.