Take the steak out of the refrigerator and let it come to room temperature while you preheat a skillet over medium-high heat.
Season the steak generously with salt and pepper on both sides.
Meanwhile, preheat your oven to 425°F. Toss the broccoli with 1 tsp olive oil, salt, and pepper, and spread on a baking sheet.
Roast the broccoli in the oven for about 15-20 minutes until tender and slightly charred, stirring halfway.
While the broccoli roasts, prepare the garlic mash by chopping the cauliflower into florets and steaming until soft (about 8-10 minutes).
In a small pan, heat the remaining 1 tsp olive oil and lightly sauté the garlic until fragrant; avoid browning.
Transfer the steamed cauliflower to a blender or use a potato masher, add the sautéed garlic, and blend or mash until smooth. Season with salt and pepper.
Return to your hot skillet and sear the steak for about 3-4 minutes per side for medium-rare, or adjust based on your preferred doneness.
Let the steak rest for 5 minutes before slicing against the grain.
Plate the sliced steak alongside the roasted broccoli and a generous serving of garlic mash, and serve immediately.