Prune, Pastis or Balthazar
Prune cannot take parties larger than 6. The waits are long even for a two or four top, as they don't take reservations.
Balthazar and Pastis take reservations. Of those, I think Pastis would be easier to reserve as it is much larger and also has a large communal table.
Large party brunches + great food is difficult but doable if you plan ahead.
Try this thread for suggestions but note that the Tasting Room location in Nolita has closed: