How to secure a jack wall to an existing wall?

I built the walls of my 12' x 12' shed before deciding what type of roof I wanted. Now I'm left with the problem of how to secure the roof to the lower walls. If I build a jack wall as shown below (image probably from this video), how would I secure the bottom plate of the jack wall to the top plate of the lower wall? I don't want the joint between the walls to be the weak link against wind.