Allow your steak to dry uncovered in fridge overnight, or pat it really dry with paper towels
cover generously with salt and pepper on both sides
Melt cooking fat of your choice in a heavy skillet (cast iron strongly recommended) over VERY HIGH HEAT
When your pan is really sorching hot, drop your steak right in and do not move it for at least 1 minute, until a nice golden crust forms.
While your steak is cooking, baste it with the hot fat. This will help cook it more gently but more importantly, it will cook it from both sides simultaneously, so you can have a beautiful crust on the exterior and cooked meat on the interior.
Flip steak and cook for an additional 30 seconds to 1 minute, depending on desired doneness.
Remove steak to a plate with kitchen tongs (do not pierce it with a fork!) and tent with aluminum foil or a dome shaped bowl or glass lid.
While steak is resting, place your skillet back over medium heat and add red onion. Immediately throw in shaved Brussels sprouts.
Cook stirring, for about 1 minute or until just softened. Adjust seasoning if needed.
Mound in the center of a plate; Slice your steak on a diagonal and arrange it right over the shaved Brussels sprouts
Sprinkle with goat cheese and chopped pistachio and drizzle a little bit of Balsamic reduction.