Place cubed potatoes in a microwave-safe bowl with 2 tablespoons water. Cover and microwave 5 minutes until just tender. Drain well and pat dry - this step is crucial for crispy potatoes.

Heat 2 tablespoons olive oil in a 12-inch cast iron skillet over medium-high heat until shimmering. Add potatoes in a single layer, season with 1/2 teaspoon salt and 1/2 teaspoon pepper. Cook undisturbed 4-5 minutes until golden on the bottom, then flip and cook another 4 minutes until crispy and tender throughout. Transfer to a plate.

Pat steaks completely dry and season both sides with 1/2 teaspoon salt and 1/2 teaspoon pepper. Add remaining 1 tablespoon oil to the hot skillet. Sear steaks 4 minutes per side for medium-rare, or until internal temperature reaches 130 degrees F. Transfer to a cutting board to rest, tenting loosely with foil.

Reduce heat to medium. Add butter to the skillet and let it foam. Add asparagus, remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Cook 3-4 minutes, tossing occasionally, until bright green and just tender with a slight bite.

Add minced garlic and thyme to the skillet. Cook 30 seconds until fragrant, stirring constantly. Return potatoes to the pan and toss everything together. Squeeze lemon juice over the vegetables and remove from heat.

Slice steak against the grain and serve over the potato-asparagus mixture, spooning any pan juices over the top. Serve immediately.