Well, it's not exactly instant, but it seems that way.
Mix a normal amount of grounds with one fourth the normal amount of water. For me that is a cup of grounds and 1 1/2 quarts of water. Cover and let sit for 12 hours. Filter and refrigerate the syrup. When you want a brew, mix one part syrup with three parts water and nuke it.
Some people recommend brewing in the refrigerator. I have tried that but I prefer it brewed at room temp. You could also buy a battery powered gizmo called Toddy, but I don't know any reason why you would need it.
I have gotten several compliments on my coffee, and I always use whatever is cheapest at the Big Lots store.