Step 1

Preheat a grill for high heat (450° to 500°F). Following the insertion guide on the Yummly Thermometer app, insert the thermometer horizontally into the thickest part of a steak until the metal is completely covered.

Step 2

Trim tops from onions and peel them, but don’t remove the root end, which will hold them together. Cut onions vertically through the root end into 8 wedges each and put them in a medium bowl.

Step 3

Rub steaks with 2 tsp. olive oil, 1 tsp. kosher salt, and 1 1/2 tsp. pepper, pressing seasonings into the meat. Gently toss onion wedges with the remaining 4 tsp. olive oil, 1/2 tsp. kosher salt, and 1/4 tsp. pepper. Set onions in a grill basket if you have one.

Step 4

Grill onions (either on the cooking grate or in the grill basket) and steaks with the lid closed, turning onions every couple of minutes and turning steaks once or twice. Cook onions until tender and lightly charred, removing them to a cutting board as done, and cook steaks until the Yummly thermometer tells you to remove the meat from the grill for your preferred doneness, 10-12 minutes total for medium-rare (130°F, which will mean 135°F after resting). Boneless steaks may be done faster. Transfer steaks to the cutting board and let them rest 5 minutes.

Step 5

Remove steaks from the bones by cutting along the bones with the tip of your knife. Cut steaks across the grain into 1/4-inch thick slices. Sprinkle with flake sea salt and serve with the onion wedges.