Prep the steak: Pat the steak cubes dry with paper towels. Dry meat sears better.
Toss with 1/2 teaspoon salt, pepper, and smoked paprika if using. Let sit at room temperature for 10 minutes while you prep the broccoli.
Prep the broccoli: If using fresh, cut into small florets so they cook quickly. If using frozen, do not thaw.
Have garlic minced and butter measured out.
Blanch or steam the broccoli (optional but recommended): Boil or steam the florets for 1 to 2 minutes until bright green and just tender. Drain well and set aside. This helps them cook fast in the skillet without over-browning the garlic later.
Heat the pan: Place a large heavy skillet (cast iron is ideal) over medium-high heat.
Add the oil and let it get hot until it shimmers. You want a strong sizzle when the steak hits the pan.
Sear the steak in batches: Add half the steak cubes in a single layer with space between pieces. Don’t crowd the pan.
Sear 2 to 3 minutes without moving for a good crust, then flip and cook 1 to 2 minutes more for medium-rare to medium. Transfer to a plate and repeat with remaining steak, adding a splash more oil if needed.
Deglaze lightly (optional): If the pan looks dry or browned bits are starting to burn, splash in 1 to 2 teaspoons water, soy sauce, or Worcestershire. Scrape up the fond with a spatula.
This adds flavor to the sauce.
Make the garlic butter: Lower heat to medium. Add butter to the skillet. When melted and foamy, stir in the minced garlic.
Cook 30 to 45 seconds, just until fragrant. Don’t let it brown.
Add the broccoli: Toss the broccoli into the garlic butter. Season with the remaining 1/2 teaspoon salt and a pinch of red pepper flakes if you like.
Cook 1 to 2 minutes until coated and warmed through.
Finish with the steak: Return the steak and any juices to the pan. Toss to coat in the garlic butter. Cook 30 to 60 seconds more to heat the steak without overcooking it.
Taste and adjust salt and pepper.
Serve: Squeeze a little lemon over the top for brightness and sprinkle with chopped parsley. Serve as is, or over rice, mashed potatoes, or cauliflower rice.