Prepare the meat: Pat the tenderloin dry with paper towels. Season generously with salt and pepper, pressing it into the surface. Let it rest at room temperature for about 30 minutes.

Make the butter: In a small bowl, mix together the softened butter, garlic, mustard, parsley, and chives until smooth. Set aside at room temperature.

Preheat and sear: Heat oven to 425°F. Place a large cast iron or oven-safe skillet over medium-high heat. Add olive oil once hot, then carefully sear the beef on all sides until a deep golden crust forms, about 2 minutes per side.

Add aromatics: Scatter the sliced shallot, sage, and oregano around the beef in the skillet.

Roast: Transfer skillet to the oven. Roast for 10 minutes, then spread half of the compound butter over the top of the tenderloin. Reduce oven temperature to 350°F and continue roasting for 15–20 minutes, basting with the remaining butter halfway through. Cook until a thermometer inserted into the thickest part registers about 125°F for medium-rare, removing it 5°F shy of your desired doneness.

Rest and serve: Tent loosely with foil and let the roast rest for 15 minutes before slicing into 1-inch thick pieces. Serve with the roasted shallots, discarding the herbs.