Trim off any excess fat from your meat and chop into small, bite-size cubes (approximately 1" x 1" inch).
Add the olive oil and butter to a large skillet over medium-high to high heat. Once the pan is hot and the butter has melted, add the steak in a single layer (work in batches if necessary). The meat should sizzle loudly when it hits the pan- if it doesn't, that means your pan isn't hot enough. Sprinkle with salt and pepper to season.
Allow the steak to cook undisturbed for at least 45 seconds or so. Check to see if the bottom side has started to brown, then flip. Continue to cook for an additional 2-3 minutes, or until the outside of the steak bites have been seared and the inside is done to your preference.
Remove steak bites to a clean plate and repeat until all steak has been cooked. Serve drizzled with homemade Chimichurri sauce (see below).
For the Chimichurri
Add the chopped parsley, garlic, shallot, oregano, red chili (or crushed red pepper), red wine vinegar, salt, and pepper to the bowl of a food processor. Process until finely minced (take care not to turn it into a thick paste from over processing).
Transfer the mixture to a clean bowl and pour the olive oil over the mixture. Gently mix to combine. Allow the Chimichurri to stand for 15 minutes, time permitting.
To make this recipe dairy-free, simply omit the butter and replace with oil.
If you prepare chimichurri ahead of time, keep stored in an air-tight container in the refrigerator until ready to use. Best if brought to room temperature before serving.
You may also use the Chimichurri Sauce as a marinade for the meat. Simply place the chopped pieces of steak in a large zip-lock bag with approximately 1/4 cup Chimichurri and mix well to coat. Marinate for at least 30 minutes to overnight in the refrigerator. Bring the steak to room temperature before cooking.