Wash and dry all produce. Adjust rack to upper position and preheat oven to 450 degrees. Trim bottom ends from baby broccoli stalks. Halve any thick stalks lengthwise, then cut baby broccoli into pieces 2-3 inches long. Halve potatoes, then place in a large bowl and toss with a drizzle of oil; season with salt and pepper.

Arrange potatoes cut-side down on a baking sheet. Roast on upper rack until just beginning to turn tender, 10-15 minutes. Remove potatoes from oven and flip on sheet. Sprinkle evenly with Parmesan. Return to oven and continue roasting until potatoes are fully roasted and cheese is crisp and browned, 8-10 minutes.

While potatoes roast, thinly slice 3 cloves garlic; halve remaining clove. Pat steak dry with a paper towel, then rub all over with halved garlic clove. Season all over with plenty of salt and pepper.

Around the time that potatoes have roasted 5 minutes, heat a large drizzle of oil in a large pan over medium-high heat. Add steak and cook until nicely browned on surface and center reaches desired doneness, 3-6 minutes per side. Transfer to a plate or cutting board, loosely cover with aluminum foil, and let rest until ready to serve. Pour out any excess oil in pan and wipe out any burnt bits.

Heat pan used for steak over medium heat. Add baby broccoli and 2 TBSP water. Cover pan and let steam 3 minutes. Uncover and increase heat to medium high. Add sliced garlic and a large drizzle of oil. Cook, tossing occasionally, until baby broccoli is browned and tender, 3-6 minutes more. Season with salt and pepper.

Divide steak between plates and dollop with garlic herb butter. Add broccoli and potatoes to the side. TIP: If any Parmesan fell onto the sheet while baking, sprinkle it over the potatoes.