Heat a little bit of oil in a cast iron skillet and sear the beef on all sides.
Add the beef, carrots, and parsnips to a lined baking tray. Drizzle the vegetables with olive oil. Season meat and vegetables with salt and pepper. Portion the butter into small cubes and place on the beef. Add a sprig of rosemary to the vegetables. Broil at 350°F for 10 minutes.
In the meantime, prepare the aioli. Add egg yolks, water, garlic, mustard, salt, and pepper into a bowl. Mix, then add the vegetable oil while stirring vigorously. Continue until you have achieved a creamy consistency.