EVERY TUESDAY for the past two years, an old man with tortoiseshell glasses has lunched at Les Arlots in Paris’s 10th arrondissement. “He sits in the same seat, at the same hour,” said chef and owner Thomas Brachet. Down a quiet street over in the 2…

EVERY TUESDAY for the past two years, an old man with tortoiseshell glasses has lunched at Les Arlots in Paris’s 10th arrondissement. “He sits in the same seat, at the same hour,” said chef and owner Thomas Brachet. Down a quiet street over in the 20th arrondissement, the same group of seven architects shows up for lunch at least once a week at La Vierge, where the menu changes everyday, making a repeat visit all the more appealing. The price tag is equally attractive. Both Les Arlots and La Vierge offer two or three courses for under 25 euros. The prix fixe, founded by the godfather of French cuisine Georges-Auguste Escoffier in the early 1900s, is nothing new. But a different kind of formule, as it’s commonly called, has emerged of late—specifically between the hours of noon and 2 p.m. on weekdays over in the les quartiers gourmands on the Right Bank. Rather than offering bargain hunters a discount for ordering multiple courses off the standard a la carte menu, these prix fixe meals stand alone. They change weekly—or more—and you’re usually spoiled silly…