your dough may have been underproofed.  That has usually been the case when my breads have a blowout like that.  I've also experienced a greater degree of oven-spring with sourdough or levain-based breads than I typically see with yeasted breads, so perhaps that is a compounding factor in your case, too.

Not much I can say about your slashing for the batard, since the evidence is pretty much destroyed.  If you are making slashes that parallel or run diagonal to the long axis of the loaf, you want to hold the blade at an angle that looks more like this _/_ than like this _l_.  There's an excellent tutorial on slashing available here.  Just click on the Handbook link at the top of the page and work your way through the table of contents to that section.

Paul

Thank you for the pointers Paul. I did make sure to hold the blade at an angle while slashing the batard, I remember so since I watched a video prior to the loaf so perhaps it is underproofing or maybe I did mess up a bit.

When I start with my Vermont Sourdough with Increased whole grain today, I'll make sure to pay even more attention to my loaf while it is on it's final fermentation.

Thanks again!

I've made a few loaves like that....

There are probably a number of factors in play here.

I think you probably added too much flour, the crumb looks heavy.  This is a common beginners issue.  Using scales, not adding much flour as you mix and knead, and learning to accept that dough will be tacky are good starting points here.

The crumb stucture is undefined, which makes me think the dough may not have been developed enough.  You might look at my videos on kneading at http://www.sourdoughhome.com/kneadingconverting.html or on the stretch and fold technique at http://www.sourdoughhome.com/stretchandfold.html

Next came what you observed, the dough tore itself apart as it baked.  That is due to extreme oven spring.  When a dough isn't allowed to rise long enough, it has more oven spring.  While some oven spring is a good thing, too much is not.  DOugh develops its flavor during its rise, and when you short change the rise, you short change yourself on flavor.  I talk about this in "The Art of the Rise" at http://www.sourdoughhome.com/theartoftherise.html

Good rise and happy baking,

Mike