Pat the sirloin steak cubes dry with paper towels, then place them in a bowl and season evenly with the fine sea salt, freshly ground black pepper, and paprika. Toss to coat and let the steak sit at room temperature while you prepare the pan.

Heat the olive oil in a large heavy skillet over medium-high heat until the oil is hot and shimmering but not smoking.

Add half of the seasoned steak cubes in a single layer, leaving a little space between each piece so they sear instead of steam. Cook for 2 to 3 minutes without moving them, then flip and cook for another 1 to 2 minutes, or until browned on the outside and cooked to your preferred doneness.

Transfer the first batch of steak bites to a plate and repeat with the remaining steak cubes, adding a little more olive oil if the pan looks dry.

Reduce the heat to medium and add 2 tablespoons of the unsalted butter to the same skillet. Once the butter has melted, add the minced garlic and cook, stirring, for about 30 seconds, just until fragrant and lightly golden around the edges.

Pour in the heavy cream, stirring to combine it with the garlicky butter and any browned bits on the bottom of the pan. Let the mixture come to a gentle simmer.

Stir in the freshly grated Parmesan cheese and cook for 2 to 3 minutes, stirring often, until the cheese has melted and the sauce has slightly thickened.

Add the crushed red pepper flakes, if using, and taste the creamy Parmesan sauce, adjusting the seasoning with a pinch more fine sea salt or freshly ground black pepper if needed.

Return the cooked steak bites and any accumulated juices to the skillet, tossing them in the creamy Parmesan sauce until they are well coated and warmed through, about 1 to 2 minutes.

Remove the skillet from the heat, stir in the remaining 1 tablespoon of unsalted butter until it melts into the sauce, and sprinkle the chopped fresh parsley over the top before serving.