Now you need to add about 3 more cups of flour. I added a little less this time, it really depends on the humidity and how exact your measurements were in the sponge step.
Once it gets too tough to stir, flip it onto a clean floured surface. Now, knead away, adding flour as you do so.
Knead the dough for 8 or 9 minutes. As my Mother says, it should be the texture of your earlobe when it's done kneading.
When you finish this part put it back in the bowl and cover it with a slightly damp towel.