Step 1: Prepare and Season the Steak
Pat the steak cubes completely dry with paper towels. This is the most critical step for achieving a proper sear. In a bowl, toss the steak with the salt, pepper, and flour (if using). The optional flour will help create a delicate, golden crust and thicken the sauce slightly. Let sit at room temperature for 10-15 minutes.

Step 2: Sear the Steak to Perfection
Heat a large cast-iron or heavy-bottomed skillet over medium-high heat until very hot. Add the high-heat oil. Working in batches to avoid overcrowding, add the steak cubes in a single layer. Do not move them for 2-3 minutes to allow a deep brown crust to form. Flip and sear the other side for 1-2 minutes for medium-rare. Transfer to a clean plate. The steak will finish cooking in the sauce. Repeat with remaining batches.

Step 3: Brown the Butter and Toast the Garlic
Reduce the heat to medium-low. Add 4 tablespoons of the butter to the skillet. Swirl until melted and begins to foam, then turn a light nutty brown and smell toasty—about 2 minutes. Immediately add the sliced garlic and red pepper flakes (if using). Cook, stirring constantly, for 45-60 seconds until the garlic is fragrant and lightly golden. Be vigilant to prevent burning.

Step 4: Create the Emulsified Sauce
Remove the skillet from heat. Add the remaining 2 tablespoons of cold butter. Swirl the pan continuously until the butter melts; this helps cool the pan and emulsify the sauce, preventing separation. The sauce should be creamy and cohesive.

Step 5: Add Parmesan and Combine
Return the skillet to low heat. Sprinkle in the grated Parmesan cheese, stirring constantly until it melts into the butter sauce, creating a rich, cheesy glaze—about 1 minute.

Step 6: Finish the Steak in the Sauce
Return all the seared steak bites and any accumulated juices to the skillet. Toss gently to coat every piece thoroughly in the garlic Parmesan sauce. Cook for 1 final minute over low heat to warm the steak through.

Step 7: Garnish and Serve Immediately
Remove from heat. Stir in the fresh parsley and a quick squeeze of lemon juice or dash of vinegar if using. Taste and adjust seasoning. Transfer to a serving platter. Garnish with extra Parmesan, a sprinkle of flaky sea salt, and more herbs. Serve instantly with lemon wedges on the side