Sprinkle the steak with salt and gently rub. Wash the salt off with warm water and pat the steak dry with a paper towel.
Cut the ribeye into 1 inch cubes.
Place all the ingredients for the marinade in a separate bowl and mix well. Give the marinade a taste and adjust accordingly if needed.
Pour the marinade over the cubed ribeye and mix to combine. Let the meat marinade for 30 minutes.
In the meantime, cut the white onion into thick slices and set it aside.
After 30 minutes, place butter in a pan to melt then place the cubed ribeye in the pan to sear for 2-3 minutes on each side, then transfer them onto a plate. Repeat until all the ribeye is seared.
Once all the ribeye is seared, place a small piece of butter into the same pan and toss the sliced onions in to cook for 3-4 minutes.
Combine the seared ribeye and onions before serving.