Launched as a Friday-only concession to jacket-averse gentlemen, La Grenouille’s “Ardoise” lunch is now offered Tuesday through Friday in the onetime artist’s studio upstairs, and is named for the slate upon which the daily-changing $29 market menu is written. No borrowed house blazers and no menu options here, but the three-course prix fixe delivers such civilized repasts as (on one recent day) celeriac rémoulade, wild salmon with braised endive, and figs in red wine, plus more ambience than you’d ever hope to find in modern-day midtown (3 E. 52nd St., nr. Fifth Ave.; 212-752-1495).