Season quail inside and out with salt and pepper; arrange them in a single layer in a large baking dish.
In a mixing bowl, whisk together the gin and oil until well blended.
Add in the onion, celery leaves, and tarragon; season with Tabasco and stir.
Pour the marinade over the quail, cover with plastic wrap, and refrigerate at least 6 hours, turning the quail twice.
Preheat oven to 350°.
Remove the quail from the marinade and wipe dry with paper towels.
Melt 4 tablespoons butter in a large cast-iron skillet over medium heat, add half the quail; brown them lightly on all sides, and transfer to a large, shallow baking dish.
Repeat with the remaining butter and quail.
Wrap each quail snugly with a strip of bacon, strain the marinade over the birds, cover them with a sheet of foil, and bake until the quail are very tender, about 45 mintues.
On a large serving platter, arrange each quail on a toast triangle and serve.