Halve garlic and wrap in foil with 1 tsp. olive oil. Leave an opening on top of foil packet. Place directly on oven rack and bake until tender and lightly browned, 12-15 minutes. Set aside. While garlic cooks, peel and cut potatoes into a 2" dice. Bring a medium pot with potatoes and enough lightly salted water to cover to a boil. Reduce to a simmer and cook until tender, 18-20 minutes. While potatoes cook, prepare ingredients.

Trim and thinly slice green onions, keeping white and green portions separate. Trim bottoms off Brussels sprouts and halve (quarter if larger than ping pong balls). In a small mixing bowl, combine blue cheese, green portions of green onions, and a pinch of pepper. Rinse steaks, pat dry, and season both sides with 1/4 tsp. salt and a pinch of pepper.

Drain fork-tender potatoes in colander. Return to pot along with roasted garlic, butter, half the milk, 1/2 tsp. salt, and a pinch of pepper. Mash with a potato masher or fork until smooth. Add remaining milk, 1 Tbsp. at a time, until potatoes reach desired consistency.

Heat 2 tsp. olive oil in a medium non-stick pan over medium-high heat. Place steaks in hot pan and sear on one side until browned, 2-3 minutes. Transfer to one side of prepared baking sheet, seared side up, and crust with blue cheese mixture.

Place Brussels sprouts and white portions of green onion on other half of prepared baking sheet. Toss with 2 tsp. olive oil, 1/4 tsp. salt, and a pinch of pepper and spread into a single layer on their side. Roast until steaks reach a minimum internal temperature of 145 degrees and sprouts are tender, 8-10 minutes. Rest steak 5 minutes before serving.

Place a serving of Brussels sprouts and mashed potatoes on a plate. Place steak next to Brussels sprouts and mashed potatoes.