B757-200 flight and cabin crews reacted to a smoking galley.

Narrative

At intermediate cruise of FL340; the #1 Flight Attendant called the cockpit concerning smoke from the #2 galley in First Class. I remained on the interphone while he attempted to locate the source and update the situation. The CB was pulled but the smoke increased. I instructed First Officer to get the QRH and don the oxygen masks and reference the smoke removal checklists. Any attempt to decrease the smoke was unsuccessful so the decision was made to land immediately. We were approximately 74 miles from ZZZ now and declared an emergency with the Center. An emergency descent was begun and the cabin crew prepared the aircraft. I made an announcement to the passengers and Flight Attendants. The approach and landing were uneventful except for the rapid descent and overweight touchdown of approximately 3;000 LBS over maximum landing weight. The Center handled the situation very professionally as did Approach and Tower at ZZZ. After landing; we cleared the runway and were inspected by the ARFF team. We then taxied to a gate where the ARFF boarded. Then passengers were deplaned through the 1L door. Then the ARFF team sprayed down the #2 oven which was still smoking and then opened the 2R door for fresh air cross ventilation.