Diner Burger & Fries

Whisk egg yolks and 1 Tbsp. lemon juice in a medium bowl. Whisking constantly, gradually drizzle in oil, drop by drop at first, until mayonnaise is thickened and smooth. Whisk in remaining 1 Tbsp. lemon juice; season with salt. Cover and chill.

DO AHEAD: Mayonnaise can be made 1 day ahead. Keep chilled.

Fit a medium saucepan with thermometer; pour in oil to measure 2". Heat over medium-high heat until thermometer registers 350°. Working in 4 batches, fry potatoes, turning occasionally, until golden and tender, 6–8 minutes; transfer to a wire rack to drain.

Just before serving, working in batches, fry potatoes until golden brown and crisp, about 4 minutes. Transfer to wire rack and season with salt.

DO AHEAD: Potatoes can be fried once 4 hours ahead. Leave on rack at room temperature.

Meanwhile, prepare a grill for medium-high heat. (Alternatively, heat a cast-iron skillet over medium-high heat.) Divide meat into 4 portions and form into into 4" patties. Using your thumb, make a small indentation in the center to help keep the burger flat as it cooks. Season generously with salt and pepper.

Grill burgers, rotating every 2 minutes, about 4 minutes per side for medium, topping with cheese during last 2 minutes of cooking.

Place burgers on buns and top with lettuce and onion. Serve with lemon mayonnaise and fries.