A Midwest-based burger chain says it will start cooking its French fries in 100% beef tallow. The change from vegetable oil to beef fat comes after Robert F. Kennedy Jr. called on McDonald's to return to the method it used for decades. Starting in February, Steak n Shake will fry its shoestring fries in beef tallow.

Beef tallow is a flavorful cooking fat obtained by slowly rendering the fat from any cut of beef. Once melted, the tallow is left at room temperature to harden and solidify, achieving a texture similar to butter.

Locations for the new restaurants have not been announced but the chain told Fox Business it was “looking at 20 priority markets and growing more in its existing regions.” It plans to open about 45 company-operated locations and as many as 40 licensed ones in 2025.

Steak n Shake, an Indianapolis-based fast-food chain with locations across the Midwest, the South and beyond, has announced plans to switch to using “100% all-natural beef tallow” when cooking its french fries,