Bring a large pot of salted water to a boil. Add linguine and cook until al dente. Reserve 1 cup of pasta water, then drain and set pasta aside.

Pat steak cubes dry with paper towels. Season with salt and black pepper evenly on all sides.

Heat olive oil in a large skillet over medium-high heat. Sear steak in a single layer for 2 to 3 minutes per side until browned. Remove and set aside.

Reduce heat to medium. Add butter to the same pan, then stir in minced garlic. Sauté for 1 minute until fragrant, and add red pepper flakes if desired.

Return steak bites to the skillet. Toss in the garlic butter and cook for 1 more minute. Remove from heat and keep warm.

In a separate saucepan, add heavy cream and grated parmesan. Cook over medium heat, stirring until smooth and creamy. Add reserved pasta water as needed to adjust the consistency.

Add the cooked linguine to the sauce and toss to coat. Season with more salt and pepper to taste if needed.

Plate the creamy linguine, then top with steak bites. Garnish with fresh parsley and more parmesan if desired. Serve hot.