I had this happen to me before on a Honda D-Series engine.
How I got it out:

The spark plug was still fine and burned fuel, so I sprayed PB blaster around the plug but into the "well" and let the engine run for about 3 to 4 minutes, long enough to warm the head but not enough to get hot.

I then use my torque ratchet set to 100 ft lbs of torque and tightened it HALF A REVOLUTION/HALF WAY FROM START then switched it back loosen and out came the spark plug.

DO NOT USE IMPACT OR ANY AIR TOOLS!!!!
DOING SO YOU RISK CROSS THREADING WHERE THAT PLUG GOES AND YOU WILL PRETTY MUCH NEED A NEW HEAD!


Her Name was Eileen, Because she most often was on a jack...