Sheet Mulching/Lasagna Gardening - When to Plant?

Will my plants grow in a lasagna/sheet mulch bed that has not decomposed much yet?
I live in central Iowa, with very good soil. I've built a large garden (4 plots, each 5 x 40 ft). I'm trying to use the lasagna gardening or sheet mulching method. I put a 9 inch layer of horse manure mixed with straw, and another 9 inch layer on top with partly decomposed leaves. According to the the book (Lasagna Gardening, Patricia Lanza), I can go ahead and plant it, which I am.
Is it really going to grow in just mulch, mostly not decomposed?
It also said I could "cook" it, by covering it with something to trap the heat to get crumbly soil in 6 weeks. I may try that on one bed. But I really would like to just plant the bed now.

 

Go for it. You will only be out a few pennies in seeds if it doesn't work.