I knew my beginning and ending before I knew my middle this year. If this happens to you as you outline that's okay. Don't panic. The middle will come as you do more exercises. (Certain plot exercises helps the outline develop.) You can use a template if you desire. I started out with the 5-point structure template and built up a middle (it seemed to jump from beginning to ending with no explanation on how it went to the ending) around it. As a plotter I do well with outlines and as I dug deeper into the prep my outline came together with a solid middle.

I don't know if you're a panster or a plotter so I don't know how detailed you want to be. Mine is very detailed. Well, right amount of details anyway it doesn't interfere with writing.