Butter 1 side the brioche slices (they'll be the outsides of the sandwiches).
Gently fold the caviar and chives into the creme fraiche.
On a clean work surface, arrange brioche buttered-side down. Place the smoked salmon on 4 of the slices and spread the creme fraiche over the others. Put the 2 together to make 4 sandwiches.
Toast the sandwiches in a large skillet over a medium heat, turning once, until golden brown. Cut the panini into wedges and serve topped with dill sprigs.
Recipe courtesy of Chef Charlie Palmer, Aureole, NYC