Preheat oven to 425 degrees F.
In a small bowl, combine 2 tbsp. of olive oil, mustard, fresh herbs and garlic until it forms a bit of a paste.
Heat an oven-safe skillet over medium high heat. Add remaining olive oil to the pan.
Pat tenderloins dry and free from moisture. Sear tenderloins a few minutes on each side until golden brown but not cooked through.
Remove the skillet from the heat. Carefully remove the tenderloins from the skillet and onto a cutting board. Brush the garlic and herb mixture evenly all over each tenderloin. Season liberally with salt and pepper.
Place tenderloins back into the same skillet and roast in the oven for about 10 - 15 minutes, or until they reach 145 degrees F.
Remove the skillet from the oven. Set the tenderloins aside and tent with aluminum foil while you make the pan sauce.
Heat the skillet over medium heat back on the stove. (Working carefully as the handle will still be hot from the stove.) Deglaze with chicken stock and scrape up all of the brown bits from the bottom.
Continue to simmer the stock until it's thickened slightly and reduced by about half. Remove the skillet from the heat and swirl in both pats of cold butter until the sauce is emulsified and glossy.
Slice the tenderloins into medallions and top with the pan sauce. Serve with your favorite sides and enjoy.