Preheat oven to 400 degrees.

Season steak heavily with salt and pepper. In a cast iron skillet over high heat, sear the steak briefly on both sides, approximately 1 minute per side. Remove from heat and let rest 5 minutes.

In the bowl of a food processor, combine all of the ingredients for the chimichurri. Pulse to combine until herbs are finely chopped. Set aside.

Cut the steak into 1 1/2” to 2” cubes. Set aside.

Roll out the puff pastry sheet slightly, keeping it in a rectangular shape. Cut the length of the rectangle into 3 rows. Cut the width of the rectangle into 4 rows.

Spread 1 tsp of chimichurri in the center of each small rectangle, leaving a small border. Place a piece of steak in the center of each.

In a small bowl, beat together the egg and water. Brush the edges of the rectangles with the egg wash. Gather the corners of each rectangle up over the piece of steak, pinching them together firmly. Place seam side down on a large greased baking sheet.

Bake for 15 to 20 minutes. Serve with remaining chimichurri.