1. Fill a large bowl with ice and water. Peel the potatoes and slice them lengthwise into ⅓ -inch thick sticks. Alternatively you can use a mandolin slicer that has a ⅜ -inch setting. Add the potatoes to the ice water and soak for 15 minutes. Drain and pat completely dry.

2. Attach a deep-fry thermometer to the side of a large, heavy pot. Add the peanut oil to the pot over medium high heat. Once the oil reaches 300°F, working in batches, carefully add the potatoes to the hot oil, and cook until beginning to soften but not browned, 3-4 minutes. Transfer the potatoes to a paper-towel-lined sheet pan.

3. Meanwhile, heat a large skillet over high heat. Pat the steak dry and season all over with 2 teaspoons salt. Add the olive oil. Once the oil is just smoking, add the steak and cook until medium-rare (see Note) about 4-6 minutes per side. Transfer the steak to a cutting board and top with the butter. Let the steak rest for 5 to 10 minutes.

4. Increase the peanut oil temperature to 350°F. Working in batches, return the potatoes to the hot oil and cook until golden brown and crispy, about 5 minutes. Transfer the fries to the paper-towel-lined sheet pan. Season with remaining ½ teaspoon salt and pepper to taste.

5. Thinly slice the steak against the grain. Serve with the frites and garlic aioli on the side.

Note: The most precise way to measure the doneness of meat is with an instant-read thermometer. For beef, rare is 125°F; medium-rare is 135°F; medium is 145°F; medium- well is 150°F; and well is 160°F. Medium-rare is our preference, but feel free to cook your steak however you like it best!