I tried to post a tutorial, but it didn't show, cause my server wasn't working and so I had to use some other crappy host...but here it is!
Sorry for no words on the tutorial...but if you can get the idea from the picture....
You would need to fold two seperate pieces of fabric into a sort of twisted half knot, then pull the two edges together and sew them. There would still be a tiny space on each side of the knot where it wouldn't be sewed completely, because the gabric has to be pulled through, but if you sew it close and tight enough, it should be just fine.
NOTE: The two pieces of fabric aren't necesarily going to be rectangles. At the bottom they will be (for the torso of the top) but to make it so it will have sleeves and fit as a shirt, you need to figure out the shape and size of the fabric.
Ignore the red lines on the top third image, i messed up and was too lazy to fix it.
I should actually try this myself and figure it out completely before posting a tutorial....but I thought I would go ahead and show you so you could figure the rest out on your own.