With the oil and beef fat still in the skillet, place the buns, cut-side down, in the skillet and cook over medium-low heat until a golden, toasty crust has formed, 2 to 3 minutes. (If you have a lot of grease in the skillet, you'll want to drain almost all of it until just a thin sheen remains before adding the buns.)☞ TESTER TIP: If you like your buns extra toasty, flip them and skillet toast the second side as well, until the buns are completely heated through, about 1 minute more.