Pat the steak cubes thoroughly dry with paper towels and season generously with salt and pepper on all sides. Let them sit at room temperature for 5 to 10 minutes.

Heat olive oil in a large skillet over medium-high heat until it shimmers. Add steak cubes in a single layer, working in batches of about 8 to 10 pieces. Sear for 2 to 3 minutes per side until a deep golden-brown crust forms. Remove cooked steak to a plate and tent loosely with foil to keep warm.

Reduce heat to medium and melt 3 tablespoons butter in the same skillet. Add 4 cloves minced garlic and sauté for about 30 seconds until fragrant and just beginning to turn golden. Return the seared steak bites to the pan and toss to coat in the garlic butter for about 1 minute.

In a separate saucepan over medium heat, melt 1 tablespoon butter. Add 2 cloves finely minced garlic and cook for 30 seconds. Pour in heavy cream and bring to a gentle simmer, stirring occasionally.

Gradually stir in freshly grated Parmesan cheese, whisking until the sauce becomes smooth and creamy enough to coat the back of a spoon. Season with salt, pepper, and optional red pepper flakes.

Pour the warm Parmesan cream sauce over the steak bites or serve on the side. Garnish with fresh chopped parsley and serve immediately while hot.