I see this all the time unfortunately.
You need this tool
You may need a long 8mm drill bit.
You need something to knock the porcelain that's stuck in the ground strap out. Most of the time when the plug breaks like that you have to chip away at it with a long punch and use compressed air to blow it out of the plug well or long needle nose pliers.
Once the porcelain is out you need to tap the group strap with a 9mmx1.0 tap.
Then it's time to use the tool. This is basically a puller. You insert the tube into the plug well and then thread the pulling tool into the ground strap.
Then you tighten the top nut by hand and the ground strap comes out.
When you go to install the new plugs coat the ground strap with silver anti-sieze.
Depending on which plug broke this can take anywhere from a few minutes to hours.
The Ford TSB.