In a deep skillet bring broth or water to a boil and add chicken breasts in one layer. Reduce heat and poach chicken at a bare simmer, turning once, 7 minutes. Remove skillet from heat and cool chicken in cooking liquid 20 minutes. Discard skin and shred chicken fine.
In a bowl, stir together chicken, half c of mayonnaise, shallot, tarragon, and salt and pepper to taste.
Make dozen sandwiches with chicken salad and bread, pressing together gently. With a 5 cm round cutter cut 2 rounds from each sandwich.
Put almonds on a small plate and spread edges of rounds with remaining half c mayonnaise to coat well. Roll edges in almonds.
Sandwiches may be made two hours ahead, wrapped in plastic wrap, and chilled.